Problem Solving

An empty reservoir has two taps for water inlet – one at the top of the reservoir and the other at the bottom. One way to fill the empty reservoir completely is to turn on the top tap only for 6 hours and then to turn on the bottom tap only for 4 hours. If the time taken by the top tap alone to fill the empty reservoir is 1.5 times the time taken by the bottom tap alone to fill the empty reservoir, how much time does it take to fill the empty reservoir if both the taps are turned on together?

A) 5 hours 20 minutes
B )5 hours 12 minutes
C) 5 hours
D) 4 hours 48 minutes
E) 4 hours 40 minutes

Answer: D

Source: e-GMAT