Pipe A can fill a tank in 12 hours and Pipe B can fill the tank in 18 hours. If both the pipes are opened on alternate hours and if pipe B is opened first, then in how much time (in hours) the tank will be full?

Options

A. `14 1/3`
B. `17 1/3`
C. `14 1/2`
D. `16 1/2`