They are supplementary angles, so they will add up to 180 degrees.
10x - 20 + 6x + 8 = 180
16x -12 = 180
16x = 192
x = 12
Now we can check:
10(12) - 20 + 6(12) + 8 = 180
120 - 20 + 72 + 8 = 180
100 + 72 + 8 = 180
172 + 8 = 180
180 = 180
x is equal to 12.
Hope this helps =)
