A tap can fill a tank in 6 hours. After half the tank is filled, three more similar taps are opened. What is the total time taken to fill the tank completely?

A 3 hours

B 3.25 hours

C 3.5 hours

D 4 hours

Correct Answer: Option E

Time taken by one tap to fill half of the tank = 3 hrs.

Part filled by the four taps in 1 hour = 4x 1/6 = 2/3

Remaining Part = 1/2