To figure this out, use the acronym SOHCAHTOA to determine which trigonometric function to use.
8 is opposite to <R and 3 is adjacent to <R so we use tangent.
Set up the following equation: tan(x)=8/3
Find the inverse (aka. tan^-1): x=69.44
So your answer is <R=69.4 degrees
Hope this helped!
