We get to use our friend SOH CAH TOA for this! (Hold back your joy ;) ). Now, for angle X, we will use TOA (Tangent = Opposite / Adjacent) because we were not given the Hypotenuse's length. We can set up the following:
Tan(x) = 4/5
When plugged into a calculator:
X = 38.66 degrees.
I hope this Helps!