Angles on a straight line are 180. Therefore, 180 - 90 (right angle) = 90
Angles in a triange add to 180.
90 + 48 = 138
180 - 138 = 42
y = 42
—————— (not sure if you need this, but:)
To work out x, you would do:
Angles on a straight line add to 180.
180 - 48 = 132
132/2 = 66
x = 66
To work out z:
Angles in a triangle add to 180. You know x is 66, so
66 + 90 (right angle) = 156
180 - 156 = 24
z = 24