Answer: D.
Step-by-step explanation: Same side interior angles are supplementary, meaning they add up to 180. Thus, we can write an equation:
<1 + <2 = 180 --> (substituting expression values)
8x + 40 + 12x + 20 = 180 --> (simplifying)
20x = 120 --> (simplifying further)
x = 60
So, D.
