Answer:
C
Explanation:
They are complementary which means they add to 90. I take it that the c is a typo and you meant x
6x + 3 + 4x + 7 = 90 Combine like terms.
10x + 10 = 90 Subtract 10 from both sides
10x = 90 - 10
10x = 80 Divide by 20
x = 80/10
x = 8