These angles are supplementary
meaning they both add up to 180 because they are on a straight line
To solve:
(10x - 20) + (6x + 8) = 180
combine like terms
(10x + 6x ) + (-20 + 8) = 180
16x - 12 = 180
add 12 to both sides
16x = 192
divide both sides by 16
x = 12
To solve for the angles, you would just take x and plug it into the angle and solve XD
Hope this helps