we have
7d-12+2d+3=18
Solve for d
step 1
Combine like terms left side
(7d+2d)+(-12+3)=18
9d-9=18
Adds 9 both sides
9d-9+9=18+9
9d=27
Divide by 9 both sides
9d/9=27/9
d=3
Explanation step by step
7d-12+2d+3=18
step 1
Group common terms
(7d+2d)+(-12+3)=18
step 2
Combine like terms
9d-9=18
step 3
Adds 9 both sides ----> by addition equality property
9d-9+9=18+9
simplify
9d=27
step 4
Divide by 9 both sides ----> by division equality property
9d/9=27/9
simplify
d=3