Answer: d=9
(3d+1)+(6d+8)=90
3d+1+6d+8=90
9d+9=90
-9 -9
9d=81
divide by 9 on both sides
d=9
Explanation: In order to solve for d, you will need to remove the parentheses, then combine like variables. Then, subtract 9 from both sides. Finally, divide by 9 on both sides. You should get d=9.