Answer:
Option C is correct
Subtracting 18 from both sides isolates the variable term
Explanation:
Given an equation:

Subtract 18 from both sides we get;
Step 1.

Simplify:
Step 2.

Divide both sides by 3 we have;
Step 3.

Simplify:
Step 4.
x = 12
Therefore, Subtracting 18 from both sides isolates the variable term in step 1 helps to solve the equation.