Hello!
I've attached a photo for reference.
Lines A and B form straight angles, which measure 180 degrees. That means that -
m∠x + m∠y = 180°
m∠y + m∠z = 180°
m∠z + 43° = 180°
43° + m∠x = 180°
Since you're trying to find z, use the solvable equation with z in it:
m∠z + 43° = 180°
180 = z + 43
137 = z
Answer:
m∠z = 137°
