Question

I need help with this question, I will post it as a photo.

Answer 1

Suppose that we defined an operation as ⊕; then, we can be defined the commutative property as shown below

$x\oplus y=y\oplus x$

This is called the 'commutative property of the operation ⊕'.

In our case, ⊕ is replaced by +, x for 15x, and y for 9; therefore,

$\Rightarrow15x+9=9+15x$

This is the 'commutative property of the addition'.