The right options are A and D.
Explanation:
1. Option A.
The action is: Add 3 to both sides. This means that we need to do the following operation:
x - 3 = 12
∴ x - 3 + 3 = 12 + 3
∴ x = 15
So, the solution of this problem is x = 15.
2. Option D.
The property is: Addition property of equality. This is the property we are chosen because we need to isolate the variable x. To do that, we need to add a number of each side of the equation to find our goal and this property allows us to get our goal.
