This is a proportionality question. We have two transversals meeting at a point; the indicated congruent angles indicates the traversals intersecting parallel lines. Usually in these sorts of questions the parallel lines are on the same side of the common vertex, but here the vertex is in between, so the x is proportional to the 42.
x/6 =42/36
x = 6(42/36) = 42/6 = 7
Answer: 7