Okay, it's very simple, to solve this triangle you need to understand what the other angles are. We know that angle A is 90º, as it is represented as a square.
We now need to solve for angle B. angle B can be solved for by
Sin (x) = Opposite / Hypotenuse = 3 / 3√5 = 2.24ish
sin(x) = 2.24
x = [tex]sin^{-1}[/tex](2.24)
Use sin.
