Problem #$4$

A tractor$-$trailer truck has a drag area C$\_($D$)$A$=8$m$^(2)$ bare and

C$\_($D$)$A$=6\mathrm{.}7$m$^(2)$ with a deflector added. Its rolling resistance

is $50$ N for each mph of speed. Calculate the total

horsepower required if the truck moves at $($a$)55$ mph ;

and $($b$)75$ mph $.$