Answer:
x = 30
Step-by-step explanation:
Given line m and line n are parallel:
x + 72 = 3x + 12 export like terms to the same side of equation with opposite indicator (- changes to + and + changes to -)
72 - 12 = 3x - x add/subtract like terms
60 = 2x divide both sides by 2
30 = x
