Answer
$P(x)=-0.0000494066006 x^3+0.004780241572 x^2$
See image
Work Step by Step
$P(x)=\frac{-2h}{l^3}x^3+\frac{3h}{l^2}x^2$
$h=6.629mi$
$l=64.5mi$
$P(x)=\frac{-2\times6.629mi}{(64.5mi)^3}x^3+\frac{3\times6.629mi}{(64.5mi)^2}x^2$
$P(x)=-0.0000494066006 x^3+0.004780241572 x^2$
