Q: Four large cheeseburgers and two chocolate shakes cost a total of $7.90. Two shakes cost 15 cents more than one cheeseburger. What is the cost of a cheeseburger? A shake?

A: I will let x=cost of cheeseburger and y=cost of shake. We know that four large cheesbeburgers and two chocolates shakes costs a total of $7.90; thus, our first equation is 4x+2y=7.90. Now, we also know that two shakes cost 15 cents more than one cheeseburger. This implies, x-2y=0.15. So, the system of equations is,

4x+2y=7.90

x-2y=0.15.

Therefore, x=$1.61 and y=$0.73.

This is not the answer in the back of the book. I am not sure what I am doing wrong.

I got the second question!

Thanks