Answer:
x = 21
Explanation:
Given line a is parallel to line b we can form the following equation to find the value of x:
6x + 12 + 2x = 180 (because these are supplementary angles and their sum is equal to 180)
add like terms
8x + 12 = 180 subtract 12 from both sides
8x = 168 divide both sides by 8
x = 21