PLEASE show calculations for every step written

A car $,($C$\_$d $=\mathrm{.}35,$ A$\_$f$=25$ft$^2,2=2500$lb$,$ and$=0\mathrm{.}002378$slug$\frac{s}{f}{t}^3$ is travelling at $90$

$m\frac{i}{h}.$ The engine develops maximum power of $126\mathrm{.}85hp.$ What is the maximum grade this

vehicle could ascend on a paved surface while its engine is developing maximum power?

$($use the relationship $F_c={550}^{**}(\frac{P**}{V})$ and $$ is $1).$