Let a be the amount of water in container A and b be the amount of water in container B, then
a = 3b
a - 1.25 = 2(b + 1.25) = 2b + 2.5
3b - 1.25 = 2b + 2.5
3b - 2b = 2.5 + 1.25
b = 3.75
a = 3(3.75) = 11.25
Thus, there are 3.75 + 11.25 = 15 quarts of water in all.
b.) Total volume after pouring lemon = 15 + 1.5 = 16.5 quarts
Total number of container needed = 16.5 / (1/2) = 2 x 16.5 = 33 containers.