The given proposition is
[tex]m\angle UJN=m\angle EJN\rightarrow m\angle UJN+m\angle YJN=m\angle EJN+m\angle YJN[/tex]
As you can observe, it was added angle YJN to the equation on both sides. The property that allows us to do that it's call addition property of equalities.
Therefore, the right answer is "addition property".
