What you're looking at in this image are two alternate exterior angles.
Alternate exterior angles, are, essentially, exterior angles of a transversal that runs through two parallel lines. These angles are on alternating sides. These angles, assuming the lines are parallel, must be equal.
There's a proof behind why these angles are equal, but I won't bore you with the specifics as the question doesn't require it.
So - we know that these two angles must be equal to prove that the lines A and B are parallel. Knowing this, we can write an equation:
5x + 20 = 3x + 60
<u>Subtract 20 from both sides:</u>
5x + 20 - 20 = 3x + 60 - 20
5x = 3x + 40
<u>Subtract 3x from both sides:</u>
5x - 3x = 3x - 3x + 40
2x = 40
x = 20
If you have any questions on how I got to the answer, just ask!
- breezyツ
