First, turn your problem into an equation.
3x - 3 = 21
x represents the unknown number.
Your goal is to solve for x.
Start by adding 3 to both sides.
3x - 3 = 21
+ 3 + 3
3x = 24
Your next step is to divide by 3.
3x/3 = 24/3
x = 8
Your answer is 8.
Your welcome!