Answer: x = 2.5 (choice D)
Explanation:
If line r and line s are parallel, then the two angles marked must be congruent. Refer to the corresponding angles theorem for more details.
This means we'll set the angles equal to one another and solve for x.
angle1 = angle2
40-4x = 50-8x
-4x+8x = 50-40
4x = 10
x = 10/4
x = 2.5
