That is the Identity Property of Addition.
If it is adding and the whole number stays the same it is Identity Property of Addition.
If it is multiplying then it would be the Identity Property of Multipulcation. For example for this problem it would be 6x1 in multipulcation in which the whole number would stay the same.
Here are descriptions of all the properties:
https://wikis.engrade.com/mathproperties1