(a)
A right angle sums to 90
6x + 4x + 10 = 90
10 x = 80
x = 8
(b) straight line = 180
5x + 13 + 3x + 7 = 180
x = 20
(c) Sum of triangle angles = 180
3x + 5 + 2x + 18 + 2x + 17 = 180
x = 20
(d) Sum of two angles in right angle = 90
90 = x + 30
x = 60
