Find x+y+z
For x:- x + 90 = 180 (Linear pair)
Or, x = 180 - 90 = 90 degree
For y:- y + 120 = 180 (Linear pair)
Or, y = 180 - 60= 120 degree
For z:- z + 30 = 180 (Linear pair)
Or, z = 180 - 30= 150 degree
So, x + y + z = 90 + 120 + 150= 360 degree
the sum of all extereior angle is 360 degrees in a polygon so x+y+z=360 degrees