You can find the answer with the steps in the app(cymath)
Answer: 22 minutes
Step-by-step explanation: 500-170 means that he drained 330 gallons of water so 330 divided by 15 gallons a minute so you get 22 so it takes 22 minutes to have 170 gallons left in the pool
Not sure of my answer but, velocity=delta d/delta t. t=delta d/ velocity
—> t=(13-3)/15=>10/15=2/3s