Answer
a decrease of 0.2 gallons per second
Explanation
The drain was open for 30 seconds.
The water that ran out for 30 seconds = 20 - 14
= 6 gallons
Rate of decrease = (change in gallons)/(time taken)
= 6/30
= 0.2
The rate of change in the amount of water remaining in the tub per second will be the same as the one that ran out since the outlet is the same.
So the correct answer from the choices is "a decrease of 0.2 gallons per second".
