Permutation

can someone help me under stand this please?

A permutation is an arrangement of all or part of a set of objects, with regard to the order of the arrangement. Each possible arrangement would be an example of a permutation.

The complete list of possible permutations would be:

AB, AC, BA, BC, CA, and CB.

Permutation is used for lists (order matters) and Combination for groups (order doesn't matter). Famous joke for the difference is: A “combination lock” should really be called a “permutation lock”. The order you put in the numbers of lock matters.

the answer is "add 2y and y"

step-by-step explanation:

you need to collect the like terms first.