A pipe can fill a tank in 0.9 hours and another pipe can empty in 0.7 hours. If tank is completely filled and both pipes are opened simultaneously then 450 liters of water is removed from the tank is 2.5 hours. What is the capacity of the tank?

Answer: Option D

Pipe A can fill the empty tank in = 0.9 hours
So work rate of the Pipe A = $$\frac{100}{0.9}$$ % per hour
Pipe B can empty the tank in = 0.7 hours
Negative Work rate of B = $$\frac{100}{0.7}$$ % per hour. (B is removing water, so, taken as negative work)
Tank fill per hour = $$\frac{100}{0.7}-\frac{100}{0.9}$$   = 31.75% per hour
Time Taken to empty the tank = $$\frac{100}{31.75}$$  ≈ 3.15 hours
So, Capacity of the tank = 3.15 × 180 = 567 liters