Chinese wall
$V = A_bL$
$A_b = \frac{1}{2}(25 + 15)(20)$
$A_b = 400 ~ \text{ft.}^2$
$L = 1500(5280)$
$L = 7\,920\,000 \text{ft.}$
$V = 400(7\,920\,000)$
$V = 3\,168\,000\,000 ~ \text{ft.}^3$
Equatorial wall
$V = A_bL$
$3\,168\,000\,000 = 4h(24\,900 \times 5280)$
$h = 6.0241 ~ \text{ft.}$ answer