In Step 3, the equation shows:
\( 6m + 12 - 12 = 5m + 7 - 12 \)
This operation involves subtracting 12 from both sides of the equation, which illustrates the principle that you can perform the same operation on both sides of an equation without changing the equality.
Thus, the property being used is the Subtraction Property of Equality.
So the correct response is:
Subtraction Property of Equality