017 Review Problem - Amount of water to fill the large network of city pipes

$V = \frac{1}{4}\pi(1^2)(400 \times 5280)$

$V = 528,000
~ \text{ft.}^3$

$V = 528,000
~ \text{ft.}^3 \times \dfrac{7.48 ~ \text{gal.}}{1 ~ \text{ft.}^3}$

$V = 12,407,531.69 ~ \text{gal.}$           answer