Final answer:
The addition property of equality was used to add 2x to both sides of the equation in Step 2, resulting in the elimination of the x term on the left side and its addition on the right side, transitioning to Step 3.
Step-by-step explanation:
The property used to go from Step 2 to Step 3 is the addition property of equality, which states that you can add the same number to both sides of an equation and the equality will still hold. In this case, the number 2x was added to both sides of Step 2:
-2x - 3 + 2x = x - 18 + 2x
This results in the x terms being eliminated on the left side and combined on the right side, hence getting to Step 3: -3 = 3x - 18.
This same property is used in other operations, such as when rearranging an equation to solve for an unknown or balancing chemical equations.