An apple has 24 fewer calories than a banana. If 7 bananas have the same number of calories as 10 apples, how many calories are in a banana?
Let A = calories in apple and B = calories in banana.
B = A + 24
7B = 10A
Substitute A + 24 for B in the second equation and solve for a.
7(A+24) = 10A
Put that value in the first equation to find B. To check, put both values in the second equation.