Yes, 90° is supplementary and 180° is condemnatory.
Hope it helps!
Not sure if your trying to solve for x or v
3(x+5)=39
3 * x + 3 * 5 = 39
3x + 15 = 39
3x = 39 - 15
3x= 24
x = 8
B. she should buy 14 yards of fabric,because 14×3=42 so there is your 42 feet.