Answer:
x = 12
Step-by-step explanation:
Complementary angles add up to have a sum of 90 degrees. We can create an equation and solve for x.
3x + 6x - 18 = 90
~Simplify
9x - 18 = 90
~Add 18 to both sides
9x = 108
~Divide 9 to both sides
x = 12
Best of Luck!
