123 is a linear pair with the inside angle so
180-124= 57. Now we have two inside angles and a triangle has to be 180 degrees so
57+42=99 we know that both angles equals 99 so
180-99=80. The third angle is 81 and is a linear pair with x soooo
180-81=99
X is equal to 99. You can also do corresponding angles and have X be 99 because of the inside angle that’s also 99