You need to distribute the 9 by multiplying it by both terms inside of the parenthesis
9 times d is 9d
9 times -1 is -9
you can rewrite the equation as
3d=9d-9
Now you can solve for d
add 9 to both sides
3d+9=9d
subtract 3d from both sides
9=6d
divide both sides by 6
d=9/6
you can reduce this to 3/2
you can also write it as a mixed number 1 1/2