Answer:
Let x be the number of calories in the pepperoni pizza and y be the number of calories in ham-and-pineapple pizza. Then, we can make two equations out of the problem statement.
Eq 1: (1/2)x + (3/4)y = 765
Eq 2: (1/4)x + y = 745
By transposing, Eq 2 becomes: y = 745 - (1/4)x. We substitute this to Eq. 1:
(1/2)x + (3/4)(745 - (1/4)x) = 765
x = 660
Then we substitute x to Eq 2 to get y:
y = 580
Thus, there is 660 calories in pepperoni pizza and 580 calories in ham-and-pineapple pizza.