A triangle is 180°. So the sum of the 3 angles should be 180°. Knowing this, you can do:
(4x + 2) + (2x) + (70) = 180
4x + 2 + 2x + 70 = 180
6x + 72 = 180 Subtract 72 on both sides
6x = 108 Divide 6 on both sides
x = 18
[proof that x = 18]
4x + 2
4(18) + 2
72 + 2 = 74°
2(18) = 36°
74 + 36 + 70 = 180
180 = 180
