A + B + C = 518 ft^3 A = 1/3B, or 3A = B B = C A + B + C = 518 ft^3 1/3B + B + B = 518 7/3B = 518 B = 518×3/7 = 222 ft^3 A = 1/3B = 1/3×222 = 74 ft^3 C = B = 222 ft^3
If 1/3 is left every hour then it would then after 3 hours wouldn't it be gone? Most would assume if only a third of the water is left every hour then after three hours there would be either of two answers if the question was written correctly: one third because they refilled it on the 2nd hour or none because it wouldn't even last two hours