Parallel lines that are crossed by a transversal (diagonal) will have angle properties that are very similar and consistent. Given that a straight line will form a total angle of 180°, the measure of ∠a would be 180 - 36 = 144°. Because ∠a and ∠b are corresponding angles so they are congruent (same measure) so ∠b = 144°. Since ∠b = 144° and is the opposite, vertical angle to ∠c, they must also be congruent as well. ∠a and ∠c are also alternate exterior angles that are congruent, so ∠c = 144° as well.
