Answer :
To solve the equation 3x + 6 = 21, follow the following steps.
Step 1: Collect like terms
"6" crosses the equality sign to the right and becomes "-6"
3x = 21 - 6
Step 2: Simplify the expression in step 1
Note that 21 - 6 = 15
The equation becomes:
3x = 15
Step 3: Divide both sides 3
The equation becomes
3x / 3 = 15/3
x = 5