Solutions: 21 and 22 are alternate interior angles therefore they are supplementary. m2 1 + m2 2 = 180 (3x+7) + = 180 (Substitution Property) 3x + 4x + 7- 2 = 180 = 180 7x + 5 - 5 = 180 - 5 7x = 175 7 7 x = angles​​