#### Answer

Commutative property of addition.

#### Work Step by Step

The commutative property of addition explained:
The sum of numbers in a particular order is the same as the sum of the same numbers but in a different order. Adding the same numbers in any order will yield only one answer.
Example: 2 + 3 +4 = 9
3 + 2 + 4 also is = 9
and 4 + 2 + 3 = 9
Similarly, as given, 3 + y = y + 3