Alright so part A wants to know how much more pizzas were cheese than pepperoni and sausage COMBINED. This means that you have to subtract the amount of cheese pizza from the amount of sausage pizza PLUS pepperoni pizza.
1/2 was cheese. 1/4 was sausage and 1/6 was pepperoni. Add 1/4 and 1/6. Get a common denominator, which in this case is 12 because 4 and 6 both go into it. So now you want to make the denominator for both of those numbers 12. To do so for 1/4, you multiply both top and bottom by 3 and you will get 3/12. To do so for 1/6, you multiply the top and bottom by 2 and you will get 2/12. Add 2/12 and 3/12 and you get 5/12. This is NOT the answer though, this is only the amount of pizzas that were sausage AND pepperoni. Now go back to the original equation, which wants to know how many more pizzas were cheese than were pepperoni and sausage. To find this, subtract 3/12 from 1/2. 1/2 equals 6/12. So 6/12 minus 5/12 equals 1/12 and that is the answer I believe.
Since a square has all equal sides, this would mean the the all the other sides are 20 as well. To get the area, you would just multiply 20 by 20 to get 400. :)
