We know: the sum of the angles measures in a triangle is 180°.
Therefore we have the equation:
64° + 75° + α = 180°
139° + α = 180° subtract 139° from both sides
α = 41°
α and ∠2 are Supplementary Angles - they add up to 180°.
α + m∠2 = 180°
41° + m∠2 = 180° subtract 41° from both sides
m∠2 = 139°
