Answer: D. Division property of equality.
Explanation:
What was done to the equation is that both sides of it where divided by 9 to solve for x.
Equations have many properties. One of those is that when we do the same operation in both sides, the equation is still an equality.
In this case, the answer would be:
D. Division property of equality.
Because this property indicates that when we divide both sides of an equation by the same number, the expression remains an equality.