hi please solve the following.

A water vendor has a tank of capacity 18900 l. the thank is being filled with water from two pipe A and B which are closed immediately when the tank is full. water flows at the rate of

1. if the tank is empty and the two pipes are opened at the same time calculate the time it takes to filled the tank.
2. on a certain day the vendor opened the pipes A and B to fill the empty tank. after 15 minutes he opened the outlet to supply water to his customer at average rate of 20 liters per minute.
3. calculate the time took to the tank on that day