Answer
$32.6^{\circ}$
Work Step by Step
First, ensure that your calculator is in radians.
On your graphing calculator, press the following sequence of buttons:
1. COS$^{-1}$
2. (
3. .8425
4. )
5. ENTER
Therefore, $arccos(.8425)=cos^{-1}(.8425)=.569$ radians. Then, convert this number to degrees by multiplying by $\frac{180}{\pi}$.
$.569radians=(.569(\frac{180}{\pi}))^{\circ}\approx32.6^{\circ}$.