Answer
Please see the work below.
Work Step by Step
We know that
$Power=\frac{Energy}{time}$
$\implies P=\frac{mgh+F_{air}d}{t}$
$P=(mgsin(\theta)+F_{air})(v)$
This simplifies to:
$sin(\theta)=\frac{(\frac{P}{v})-F_{air}}{mg}$
We plug in the known values to obtain:
$sin(\theta)=\frac{(3800)(\frac{60}{3.6})-450}{(1400)(9.8)}$
$sin(\theta)=0.1334$
Now the angle is:
$\theta=sin^{-1}(0.1334)$
$\theta=7.7degrees$
