Answer:
Distributive Property of Multiplication over Addition
Explanation:
Robert multiplied the 3 by everything in the parenthesis, so
3*x=3x
and
3*2=6
This is called the Distributive Property. To be more specific, he is multiplying 3 by two the terms being added in the parenthesis, which is x+2.
This is called the Distributive Property of Multiplication over Addition.