So there are three ways to do this. If you have 2 sides of the triangle you can use SOH-CAH-TOA to find the other angles. S= sin, O= opposite side of the angle, H= hypotenuse. The hypotenuse is the longest side of the triangle. C= cos, A= adjacent, adjacent means the side next to the angle, H= hypotenuse. T= tangent, O= opposite, A= adjacent. You could take 180 and subtract 55 to figure out what you have left then you can figure out what you need to do next. The other way that I can think of is to use the law of sines which is sin A/ A, Sin B/B, Sin C/C. You can use this to equal Sin A/A = Sin C/ C or any combination as long as you don't mix them together like Sin A/ C because it just wouldn't work. Sin= the angle and A,B, and C equals the sides so if you say Sin A you are saying angle A. This can work if you have two sides. You would set it up as Sin 55/what ever side is A which is = to let's say Sin C/ whatever side is C. Then you can cross multiply to say whatever side is C sin 55/whatever side is A = Sin C then you use your calculator to Sin-1 the answer to get what the angle of C is. Then add them together and subtract from 180 for the last angle.