To solve for x in this triangle you can find the sizes of the other angles on the triangle and subtract them from 180. In this triangle only one measure is given, 120. However, there is another angle that can be figured out based on the information given. Since there is an exterior angle of 140 degrees that lies on a straight line, the angle next to it is 40 degrees because two angles that lie on the same straight line adjacent to each other will always add up to 180 degrees. Now we can add 120 degrees and 40 degrees to each other to get 160 degrees excluding the missing angle. Now to solve for the measure of the missing angle, subtract 160 from 180 to get 20 degrees as triangles always have their angles adding up to 180 degrees. Now to solve for x, divide 20 by 10 to get 2. Sorry for the wall of text lol.
