We know that all angles of a triangle equal 180 when added together. We have two angle measures which are 3/2x and 1/2x
***3/2x + 1/2x + x = 180 degrees***
For the other way you can switch around the positions of the angles in the equation as long as the = stays 180 so like
X + 3/2x + 1/2x = 180
180 + x + 1/2x + 3/2x
Or maybe change the 3/2x to 1 1/2x