x = 65.22°
Here's the work!
Because we are finding the measure of the angle and not a side, we need to use the inverse functions of trigometry.
In this case it's tan^-1 because we are given the opposite (13 is the opposite) and adjacent side (6 is the adjacent side).
So he equation we have is tan^-1 (x°) = 13 / 6.
In order to get x by itself, we can multiply tan^-1 to 13/6.
Our equation now looks like x° = tan^-1 (13 / 6)
Put it right into the calculator and we get 65.22°!
Hope I've helped! I've attached an image of my work in case you need to copy it.
:D