Two pools are being filled with water. to start, the first pool contains 890 liters of water and the second pool is empty. water is being added to the first pool at a rate of 20.5 liters per minute. water is being added to the second pool at a rate of 42.75 liters per minute.

Let x=amount of time it takes both pipes draining together to empty the pool 
First pipe empties at the rate of 540,000/150=3600 liters/min
Second pipe empties at the rate of 540,000/225=2400 liters/min 
Together, both pipes empties at the rate of 3600+2400=6000 liters/min, so our equation to solve is: 
6000*x=540000