Answer:
x = 10
Step-by-step explanation:
To make A // B, corresponding angles should be congruent.
9x - 40 = 3x + 20
Subtract 3x from both sides
9x - 3x - 40 = 20
6x - 40 = 20
Add 40 to both sides
6x = 20+40
6x = 60
Divide both sides by 6
x = 60/6
x = 10
