For what value of x is line a parallel to line b? enter your answer in the box. x =

It will be parallel only if angle (2x + 20) equal to 80, or (2x + 20) + 100 equal to 180. Let's use the first example:
1) 2x + 20 = 80
Subtract 20 from the each side:
2) 2x = 80 - 20
3) 2x = 60
Divide everything by 2:
4) 2x/2 = 60/2
5) x = 30
So, the answer will be x = 30. Hope this helps!