C. Adding 18 to both sides isolates the variable term.
Your end goal is to isolate “x” which is a variable. However, the variable is multiplied by 6 and is “6x” making it a variable term. You must first isolate the variable term before you can isolate the variable itself. So step 1 is to add 18 to both sides (cancelling it out on the left side of the equals sign), thus isolating the variable term.
