A pool has a capacity of 4,000 litres. Mr. Osborne starts filling the empty pool with water at a rate of 20 L/min. The pool springs a leak after 20 minutes and water
leaks out at 2 L/min. Beginning from the time when Mr. Osborne starts filling the
empty pool, how long does it take until the pool is completely full?
A 4 hours
B 3 hours 20 minutes
C 3 hours 40 minutes
D4 hours 20 minutes
E 3 hours