A rectangular tank, 32in long, 20in wide and 15in high, is filled with water up to 3/8 of its height. If the tank is going to be filled by water from a tap flowing at 5 cubic inches a minute, how much time is needed to fill the rest of the tank?

It needs minutes to fill up the tank.

The volume of the tank

32 in × 20 in × 15 in = 9600 in^{3}

Filled water:

9600 in^{3} × 3/8 = 3600 in^{3}

Need to be filled:

9600 - 3600 = 6000 in^{3}

6000 ÷ 5 = 1200 minutes

It will take 1200 minutes to fill up the tank.