Answer:
By definition, if two angles are complementary, they both will add up to 90 degrees. Knowing this add 18 and (6d-6) together to equal 90.
18+(6d-6)=90
Subtract 18 from both sides, then add 6. This leaves you with 6d equal to 78. Divide by 6 to get 13.
(6d-6)=72
6d=78
d=13 degrees
Make sure of your answer. You know that d is 13, so plug it back into the equation to see if it equals 90 degrees.
18+6(13)-6=90
18+78-6=90
90=90