We have boxes colored either red or blue. In each blue box there is a fixed number of blueberries. In each red box there is a fixed number of strawberries. If we dispose of one blue box for one additional red box, the total number of berries would increase by 10, and the difference between the total number of strawberries and the total number of blueberries would increase by 50. Each blue box contains how many blueberries?	Choose one:
A) 10
B) 15
C) 20
D) 25
E) 30

Rationale: "let x be the number of blueberries in each blue box . then there are x + 10 strawberries in each red box . x + ( x + 10 ) = 50 x = 20 the answer is c ."
Answer: C