Answer
$\theta=21.0^{\circ}$
Work Step by Step
To find the work done my a constant force, use the formula $$W=Fdcos\theta$$ Solving for $\theta$ yields $$\theta=arccos(\frac{W}{Fd})$$ Substituting known values of $F=75N$, $W=3500J$, and $d=50.0m$ yields an angle of $$\theta=arccos(\frac{3500J}{(75N)(50.0m)})=21.0^{\circ}$$
