Answer:
72°
Step-by-step explanation:
Since c||d, ∠3 would be the same as ∠1
Since those two are supplementary angles, subtract 180 with 108 to get the measure of ∠1 which is 72°.
Since ∠1 and ∠3 are corresponding angles, they'll be congruent meaning ∠3 is also 72°.
