Two taps A and B can fill a tank in 5 hours and 20 hours respectively. It both the taps are open then due to a leakage, it took 30 minutes More to fill the tank. If the tank is full, how long will it take for the leakage alone to empty the tank? `4 1/2h r s` b. `9\ h r s` c. `18\ h r s` d. `36\ h r s`