ANSWER:
-1080 gallons
Explanation:
If the volume of water in the pool changes by -12 gallons per minute, what we must do is multiply -12 by the elapsed time, in this case it would be 90 minutes to determine how much it will change after 90 minutes. Just like that:
![\Delta v=90\cdot-12=-1080](https://img.qammunity.org/2023/formulas/mathematics/college/8turuo981s8bx06u9cs3hul6xup8exyv47.png)
Which means that the change in volume after 90 minutes is 1080 less gallons.