These angles are corresponding angles. Therefore, we would use the Corresponding Angle Theorem to solve. (:
Corresponding angles are equal to each other. Knowing this we can set each expression to each other.
3x + 11 = 4x - 21
x = 32
Substitute to check your answer. If the value of x is 32 both expression will equal the same number.
3x + 11
3 (32) + 11
96 + 11
107°
4x - 21
4 (32) - 21
128 - 21
107°
I hope this helps. (:
