Given:
lines a and b are parallel.
So, the alternative angles are congruent
So, the measure of the angle that is supplementary with x = 120
the supplementary angles have a sum of 180
so, we can write the following equation:
[tex]\begin{gathered} x+120=180 \\ x=180-120 \\ x=60 \end{gathered}[/tex]
So, the answer will be: 60 deg
