SQL Funtions and triggers

Here we go,
 
I have a write a stored function called get_project_cost. This function takes as input a project title and returns teh cost to date for that project. NOte that the type for cost is 'number'.Call the function from within an SQL statement to give the project title,customer name and cost to date for project.

I am struck.

Moreover, I have to write a trigger as well.