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Suppose that we defined an operation as ⊕; then, we can be defined the commutative property as shown below
[tex]x\oplus y=y\oplus x[/tex]This is called the 'commutative property of the operation ⊕'.
In our case, ⊕ is replaced by +, x for 15x, and y for 9; therefore,
[tex]\Rightarrow15x+9=9+15x[/tex]This is the 'commutative property of the addition'.