I have a question adding a change to a php file

I have this Extenaion that I bought, but can not seem to get a hold of the programmer. And I have to edit a php file and add to it and I am really not sure where I have to add the change. Here is the change I have to Make and I have attach the php file.

 open "catalog/model/catalog/category.php" and add these 2 functions in existing class

public function GetLinkHrf($p_id)
{
 $query = $this->db->query("SELECT DISTINCT * FROM " . DB_PREFIX . "category c LEFT JOIN " . DB_PREFIX . "category_description cd ON (c.category_id = cd.category_id) LEFT JOIN " . DB_PREFIX . "category_to_store c2s ON (c.category_id = c2s.category_id) WHERE c.category_id = '" . (int)$p_id . "' AND cd.language_id = '" . (int)$this->config->get('config_language_id') . "' AND c2s.store_id = '" . (int)$this->config->get('config_store_id') . "' AND c.status = '1' order by c.sort_order");
 $quick_array = $query->rows;
   $main_id = $quick_array[0]['category_id'];
   $parent_id = $quick_array[0]['parent_id'];
   if($parent_id=='0')
   { $href[] = $main_id; }
   else
   {
	 $href[] = $main_id;
	 $href[] = $this->model_catalog_category->GetLinkHrf($parent_id); 
      }
   $array_rev = array_reverse($href);
   $link = implode("_",$array_rev);
   return $link;
}
public function getSubCategoryData($pid)
{
  $return_strings = "";
  $query = $this->db->query("SELECT DISTINCT * FROM " . DB_PREFIX . "category c LEFT JOIN " . DB_PREFIX . "category_description cd ON (c.category_id = cd.category_id) LEFT JOIN " . DB_PREFIX . "category_to_store c2s ON (c.category_id = c2s.category_id) WHERE c.parent_id != '0' and c.parent_id = '" . (int)$pid . "' AND cd.language_id = '" . (int)$this->config->get('config_language_id') . "' AND c2s.store_id = '" . (int)$this->config->get('config_store_id') . "' AND c.status = '1' order by c.sort_order");
  if($query->rows){
  $return_strings .= "\n\n<ul>";}
  $counter = 1;
  foreach ($query->rows as $result) 
	{ 
	  $ppid = (int)$result['category_id'];
	  $query_sub = $this->db->query("SELECT * FROM " . DB_PREFIX . "category WHERE parent_id = '$ppid'");
	  $ppid_link = $this->model_catalog_category->GetLinkHrf($ppid);
	  $return_strings .= "<li><a href='".$this->url->link('product/category', 'path=' . $ppid_link)."'>".$result['name']."</a>";
	  if($query_sub->rows)
		{ 
		   $return_strings .= $this->model_catalog_category->getSubCategoryData($ppid); 
		}
	  else
		{ 
		   $return_strings .= "</li>\n"; 
		}	  
	$counter++;
	 }
	if($query->rows){ $return_strings .= "</ul>\n"; }
return  $return_strings;
}

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##category.php (same as attached file)

<?php
class ModelCatalogCategory extends Model {
	public function getCategory($category_id) {
		$query = $this->db->query("SELECT DISTINCT * FROM " . DB_PREFIX . "category c LEFT JOIN " . DB_PREFIX . "category_description cd ON (c.category_id = cd.category_id) LEFT JOIN " . DB_PREFIX . "category_to_store c2s ON (c.category_id = c2s.category_id) WHERE c.category_id = '" . (int)$category_id . "' AND cd.language_id = '" . (int)$this->config->get('config_language_id') . "' AND c2s.store_id = '" . (int)$this->config->get('config_store_id') . "' AND c.status = '1'");
		
		return $query->row;
	}
	
	public function getCategories($parent_id = 0) {
		$query = $this->db->query("SELECT * FROM " . DB_PREFIX . "category c LEFT JOIN " . DB_PREFIX . "category_description cd ON (c.category_id = cd.category_id) LEFT JOIN " . DB_PREFIX . "category_to_store c2s ON (c.category_id = c2s.category_id) WHERE c.parent_id = '" . (int)$parent_id . "' AND cd.language_id = '" . (int)$this->config->get('config_language_id') . "' AND c2s.store_id = '" . (int)$this->config->get('config_store_id') . "'  AND c.status = '1' ORDER BY c.sort_order, LCASE(cd.name)");

		return $query->rows;
	}
	
	public function getCategoryFilters($category_id) {
		$implode = array();
		
		$query = $this->db->query("SELECT filter_id FROM " . DB_PREFIX . "category_filter WHERE category_id = '" . (int)$category_id . "'");
		
		foreach ($query->rows as $result) {
			$implode[] = (int)$result['filter_id'];
		}
		
		
		$filter_group_data = array();
		
		if ($implode) {
			$filter_group_query = $this->db->query("SELECT DISTINCT f.filter_group_id, fgd.name, fg.sort_order FROM " . DB_PREFIX . "filter f LEFT JOIN " . DB_PREFIX . "filter_group fg ON (f.filter_group_id = fg.filter_group_id) LEFT JOIN " . DB_PREFIX . "filter_group_description fgd ON (fg.filter_group_id = fgd.filter_group_id) WHERE f.filter_id IN (" . implode(',', $implode) . ") AND fgd.language_id = '" . (int)$this->config->get('config_language_id') . "' GROUP BY f.filter_group_id ORDER BY fg.sort_order, LCASE(fgd.name)");
			
			foreach ($filter_group_query->rows as $filter_group) {
				$filter_data = array();
				
				$filter_query = $this->db->query("SELECT DISTINCT f.filter_id, fd.name FROM " . DB_PREFIX . "filter f LEFT JOIN " . DB_PREFIX . "filter_description fd ON (f.filter_id = fd.filter_id) WHERE f.filter_id IN (" . implode(',', $implode) . ") AND f.filter_group_id = '" . (int)$filter_group['filter_group_id'] . "' AND fd.language_id = '" . (int)$this->config->get('config_language_id') . "' ORDER BY f.sort_order, LCASE(fd.name)");
				
				foreach ($filter_query->rows as $filter) {
					$filter_data[] = array(
						'filter_id' => $filter['filter_id'],
						'name'      => $filter['name']			
					);
				}
				
				if ($filter_data) {
					$filter_group_data[] = array(
						'filter_group_id' => $filter_group['filter_group_id'],
						'name'            => $filter_group['name'],
						'filter'          => $filter_data
					);	
				}
			}
		}
		
		return $filter_group_data;
	}
				
	public function getCategoryLayoutId($category_id) {
		$query = $this->db->query("SELECT * FROM " . DB_PREFIX . "category_to_layout WHERE category_id = '" . (int)$category_id . "' AND store_id = '" . (int)$this->config->get('config_store_id') . "'");
		
		if ($query->num_rows) {
			return $query->row['layout_id'];
		} else {
			return false;
		}
	}
					
	public function getTotalCategoriesByCategoryId($parent_id = 0) {
		$query = $this->db->query("SELECT COUNT(*) AS total FROM " . DB_PREFIX . "category c LEFT JOIN " . DB_PREFIX . "category_to_store c2s ON (c.category_id = c2s.category_id) WHERE c.parent_id = '" . (int)$parent_id . "' AND c2s.store_id = '" . (int)$this->config->get('config_store_id') . "' AND c.status = '1'");
		
		return $query->row['total'];
	}
}
?>

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category.php