in the figure a)
y + 105 = 180 ( being linear pair )
y = 180 - 105
y = 75
Now
z = y ( being alternate angle )
z = 75
Also
x = z ( being vertically opposite angles)
x = 75
in the figure b)
we can see it is an isosceles triangle then
60 + 60 + z = 180 ( sum of angles of triangle)
120 + z = 180
z = 180 - 120
z = 60
now
y + 60 = 180( being linear pair)
y = 180 - 60
y = 120
also
x + y = 180( being co interior angles )
x + 120 = 180
x = 180 - 120
x = 60