Answer:
13
Step-by-step explanation:
So the concept is that co-interior angles add up to 180 in parallel line. This means:
3x + 9 + 9x + 15 = 180
So we solve for x.
12x + 24 = 180 ( What I did was simplifying the equation).
12x + 24 - 24 = 180 - 24
12x / 12= 156 / 12
x = 13
HOPE THIS HELPED
