Simonne used the following steps to simplify the given expression.

12 - 3(-2x + 4)

Step 1: 12 + (–3)·(–2x) + (–3)·(4)
Step 2: 12 + 6x + (–12)
Step 3: 12 + (–12) + 6x
Step 4: 0 + 6x
Step 5: 6x

What property of real numbers was used to transition from Step 3 to Step 4?