Mathematics · Pipes and Cisterns

A tank has three pipes - Pipe X, Pipe Y and Pipe Z attached. Pipe X and Pipe Z alone can fill the tank completely in 4 hours and 8 hours respectively. Pipe Y can empty the tank in 6 hours. Initially the tank is empty. The three pipes are operated in the following sequence. In the first hour, only Pipe X is opened. In the second hour, Pipes X and Y are opened. In the third hour, only Pipe Y is opened. In the fourth hour, Pipes Y and Z are opened. In the fifth hour, only Pipe Z is opened. This cycle of 5 hours is repeated. After how many hours will the tank be completely filled for the first time?