How do I retrieve the individual results of an array?

Here's my function:

public function pref_reference() {

	global $mysqli;

	$sql="select preferences.email, preferences.id as pref_id, preferences.tool_id, preferences.tool_fields, tools.tool_name, tools.id from preferences inner join tools on preferences.tool_id=tools.id where preferences.id='$_GET[id]'";
	if(!$query=$mysqli->query($sql))
		{
			$err='query_failure:'
			.'ERRNO: '
			.$mysqli->errno
			.'ERROR:'
			.$mysqli->error
			.PHP_EOL
			.' QUERY: '
			.$query
			.PHP_EOL;
			trigger_error($err, E_USER_WARNING);
		}
	
		$result_array=array();

	while($row=$query->fetch_array())
		{
		$result_array[]=$row;
		}
		
	return $result_array;

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I want to retrieve from this array the email address and the tool id.

So, I've got this:

$new_tool = new ToolAdmin; //call my class

$reference=$new_tool->pref_reference(); // call the above method

Now I want to echo just the email address that's a part of this array. I've tried:

$reference['email_address'], $reference[0] and just about any other combo I can think of. I know I'm missing something, but I can't figure out what.

I know how to do a foreach, but is there a more direct way of just being able to reference specific values within the array?