Answer:
x = 35
Step-by-step explanation:
Supplementary angles add up to 180°.
if (3x + 15)° and 60° are supplementary, then
3x + 15 + 60 = 180
now, you just have to solve the equation.
3x + 75 = 180
3x = 105
x = 35
Check
3*35 + 15 + 60 = 180
105 + 15 + 60 = 180
180 = 180
