Correct option is E
Time taken by pipe B to fill the tank = 72 ×5/4 = 90 hours
Capacity of tank = 360 unit (LCM of 72 & 90)
Efficiency of pipe A = 360/72=5 unit/hour
Efficiency of pipe B = 360/90 = 4 unit/hour
Required time =360 ×2/5×1/9=16 hours