Help

If that bottom angle is 90 degrees then you have two angles and you can just use angle sum of a triangle.

180-90-45=45 degrees

Otherwise you do not have enough information.  You need to know 3 things about you triangle to find a fourth.

Remember these relationships: Sine(x)=Opposite side/Hypotenuse: Cosine(x)=Adjacent side/Hypotenuse: Tangent(x)=Opposite side/Adjacent side. "Opposite" means opposite the angle that you have. "Adjacent" means one of the sides that forms the angle.

So, in your picture of angle "A", Opposite would be the "x" side, and the base where you have 8 is the Adjacent side. You have to memorize these important relationships.