x=6
(6x+4) = (8x-8)
∠3 and ∠6 have to be equal since they are opposite interior angles (these angles are always equal to each other). Opposite interior angles prove that two lines are parallel if they are equal, so you just set them equal to each other and solve for x.
(6x+4) = (8x-8)
-6x -6x
4 = (2x-8)
+8 +8
12 = 2x
/2 /2
6 = x
CHECK
(6x+4) = (8x-8)
(6[6]+4) = (8[6]-8)
(36+4) = (48-8)
40 = 40
