Question

For what value of x is line a parallel to line b?

Answer 1

The correct answer is  x=20
Enter 20 in the  box
5x+15=1155x=100x=20
and to check (5x +15) = 115 are corresponding angles(5)(20)+15 Substitute x for 20=115

Answer 2

Check the picture below.

now, if those two angles are corresponding, that means they're equal, therefore then

5x + 15 = 115

and surely you know what "x" is, and for that value, the angles are corresponding and therefore the lines are parallel.