There are 12 pipes to fill a tank and each pipe can pump 30 litres per min. If the first pipe is opened at 6:00 am and the remaining pipes are opened one after the other at regular intervals of 5 minutes, the tank is filled by 7:30 am. What is the capacity of the tank?

1) 21600 lit
2) 20000 lit
3) 22500 lit
4) 25600 lit