Answer
The incline makes an angle of $17.46^{\circ}$ with the horizontal.
Work Step by Step
The stump grinder's weight of $60.0~lb$ is directed straight down. The force of $18.0~lb$ is directed up the incline at an angle of $\theta$ above the horizontal.
We can draw a right angle triangle with $60.0~lb$ as the hypotenuse of the triangle and the force of $18.0~lb$ opposite the angle $\theta$.
We can find $\theta$:
$sin~\theta = \frac{18.0}{60.0}$
$\theta = arcsin(\frac{18.0}{60.0})$
$\theta = 17.46^{\circ}$
The incline makes an angle of $17.46^{\circ}$ with the horizontal.
