Two inlet pipes, A and B, can fill an empty tank in 22 and 33 hours respectively. They are opened simultaneously but pipe A is closed 3 hours before the tank is filled. How many hours will it take to fill the tank?

Let T be total time. A works for (T-3) hours, B works for T hours. A's rate = 1/22 tank/hour, B's rate = 1/33 tank/hour. (T-3)/22 + T/33 = 1. Multiply by LCM 66: 3(T-3) + 2T = 66, so 3T - 9 + 2T = 66, 5T = 75, T = 15 hours. This matches option D. Verification: A works 12 hours, completing 12/22 = 6/11 of tank. B works 15 hours, completing 15/33 = 5/11 of tank. Total = 11/11 = 1 tank.