Ok so first, write down the equation. We know that x=3 and y=4. You just basically plug in the terms into the variables. So it would be 3(3)+1/4(4)^2. Simplify that equation and you should get your answer :)
Take Saturdays total of $620 and subtract Fridays total of $460 to get $160. Divide that by the difference of the number of pies sold on Friday and Saturday to get $8. Take the $8 and multiply by number of pies sold on Friday (20) to get $160. Take that number and subtract it from the total sold on Friday ($460) to get $300. Divide that by how many cakes were sold on Friday (30) and get $10.
So therefore:
Pies - $8 each
Cakes - $10 each
50 out of 100 is half of the class; half of the circle will represent students going to college. 25 is a quarter of the class; a quarter of the circle will represent students not going to college. 25 is a quarter of the class; a quarter of the circle will represent students undecided about going to college.
The circle graph should look something like this: