To begin solving this question, I'm going to find the total volume of the pool. Since it is a rectangular prism we get the volume by multiplying the length by the width by the depth.
[tex]V=45\times20\times5=4500[/tex]Now, we know the pool starts with 4500ft³ water. Then it starts to lose 250ft³ each hour. If we divide the total volume by the rate, we're going to find the amount of time needed to empty the pool.
[tex]\frac{4500}{250}=18[/tex]It is going to take 18 hours!
