A water tank initially contains 180 L of water. Now, equal rates of cold and hot water enter the tank for a period of 25 minutes while warm water is discharged from the tank at a rate of 50 L/min. The amount of water in the tank at the end of this 25-min period is 40 L. What is the rate of hot water entering the tank? a) 33 L/min b) 11 L/min c) 7 L/min d) 5 L/min e) 22 L/min