Answer:
600 minutes
Step-by-step explanation:
The total rate of the Pump is gotten first
15 + 20 = total rates of 35 gallon per hour .
rate = volume/ time.
Volume = rate * time
21,000 = 35 * t
t = 21,000/35
t = 600 minutes.
To check the volume each pump will pump out.
pump A 15 * 100 = 9000 gallons
Pump B 20 * 600 = 12000 gallons.
12,000+9,000= 21,000 which gives the total gallons of the swimming pool back