A straight line is 180°.
65°, 31°, and 2y° make/add up to the 180°. So you can do:
65 + 31 + 2y = 180
96 + 2y = 180 Subtract 96 on both sides
2y = 84 Divide 2 on both sides
y = 42
A triangle is also 180°.
(4x - 1), 90°, and 31° make/add up to the 180°, so you can do:
(4x - 1) + 90 + 31 = 180
4x - 1 + 90 + 31 = 180
4x + 120 = 180 Subtract 120 on both sides
4x = 60 Divide 4 on both sides
x = 15
