Which property justifies this statement if 4x=20 then x=5

We are given the equation:

4 x = 20

To get to x = 5, what was did was to divide both sides by 4. That is:

4 x / 4 = 20 / 4

x = 5

Therefore in this case, the property which justifies the statement is the Division Property of Equality. Which states if one side is divided by a number, then the other side should be also divided with the same number.