Question

Which property is used in the statement? If z=3+1, then 3+1=z

Answer 1

This is the symmetric property of equality, and in a more general form it can be written  as: if a=b then b=a.

This  is not to be confused with communicative property,  which says that the order doesn't  matter in some operations, such as addition, and can be written as a+b=b+a