Answer:
x = 20
Explanation:
Lines l and m are parallel so the sum of given angles is = 180
3x + 12 + 5x + 8 = 180 add like terms
8x + 20 = 180 subtract 20 from both sides
8x = 160 divide both sides by 8
x = 20 replace x with 20 in given expression to calculate any measure.