• y is vertically opposite to the one whose measure is 43º.
So,
y = 43º.
• x and y are supplementary angles:
x + y = 180º
x = 180º – y
x = 180º – 43º
x = 137º.
• z and x are vertically opposites.
So,
z = x
z = 137º <——— this is the answer.
I hope this helps. =)