We start with the following fact: ∠1 and ∠2 are supplementary angles Therefore, the following equation is valid: m∠1 + m∠2 = 180 We clear the angle 2: m∠2 = 180-m∠1 Substituting values: m∠2 = 180-120 m∠2 = 60 Then, we have: ∠2 and ∠4 are vertical angles Vertical angles are a pair of angles (not adjacent) opposed to each other when two lines intersect Thus: m∠2 = m∠4 = 60 Answer: the measure of ∠4 is 60 °
