I'm quite a bit behind due - can someone ? (: go into detail, preferrably on paper, but if not, that's okay, too.

You align them ans combine the like terms 

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. (:

Is there a picture because i cannot answer it sorry