Answer:
This is actually pretty easy.
(3x + 15) = 120
3x = 105
x = 35
Step-by-step explanation:
Supplementary means angles that add up to 180 degrees... so
3x+15+60=180
15+60=75
3x+75=180
Subtract 75 from each side to get..
3x=105
Divide 3x on each side to get...
X=35
