Phil and matt make cookies for a fundraiser at their school -phil made 25% more cookies than matt -they sold the cookies for 0.25 each -after the sale, 20% of the total cookies remained. create an equation to represent the total amount of money matt and phil earned at the fundraiser based on the number of cookies matt made. explain why

The equation would be y=0.45x.

Let x be the number of cookies Matt made.  Since Phil made 25% more, and 100%+25%=125%=125/100=1.25, the number of cookies Phil made can be represented by 1.25x.

Together the cookies they made are represented by x+1.25x=2.25x

Since there were 20% of the cookies remaining, this means they sold 100%-20%=80%=80/100=0.8 of the cookies:
0.8(2.25x) = 1.8x

Each cookie sold for 0.25, so we have
0.25(1.8x) = 0.45x

Letting y be the money they make, we have
0.45x=y