Answer:
x = 30
Step-by-step explanation:
The 2 given angles are same- side exterior angles. That is they are on the same side of the transversal and outside the parallel lines.
same- side exterior angles are supplementary, thus
x + 12 + 3x + 48 = 180, that is
4x + 60 = 180 ( subtract 60 from both sides )
4x = 120 ( divide both sides by 4 )
x = 30
