So a straight line must have an angle degree measurement of 180 degrees.
So you can see that z shares a straight line with an angle with a measure of 43 degrees.
So therefore 43 + z must equal 180 degrees.
43 + z = 180
Then subtract 43 from both sides
z + 43 - 43 = 180 - 43
z = 137
So z = 137 degrees.
