Firstly you have to identify your known values and their correspondence with each other. To find “X” we will have to find the rest of the angle measurements in the triangle. Since one side is known which is the angle measuring 55 degrees we will have to find the other missing side to find X. This is where you use the angles correspondence with known values. The missing angle’s relationship with the angle measuring 80 degrees is Alternate Interior. This means they will both equal the same thing so the other missing side is 80. Now since we know all the angles for the triangle except X we will make them equal up to X. So basically 180=80+55+X. Once solved the answer is 45 degrees.