Answer: C) x = 43
This is because the two angles shown are vertical angles. Vertical angles are always congruent.
A short proof of this claim is to let y be the angle to the right of angle x. Note how x+y = 180. Then note how y+43 = 180 as well. Since the two left hand sides are equal to 180, this must mean x+y = y+43. Subtract y from both sides and we end up with x = 43. The "43" can be any positive number you want, as long it's less than 180 of course, and the same idea applies.