In this equation, they are doing the commutative property. Commutative property is a property that the numbers on which we operate can be moved or swapped from their position without making any difference to the answer. The Associative Property of Addition is a property which means that rearranging the parentheses in an expression will not change the result. Clearly, they didn’t do that; they just switched the 7 and x around which is the commutative property.
This might be slightly confusing but I hope this helps :’)
