I don't know how to set up a diagram for this, but I could write an expression. 20*4= x sorry, but I hope this helps. I not even sure my expression is correct.
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