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A student has (correctly) simplified an algebraic expression in the following steps. Between each pair of steps, identify the algebraic property that justifies moving from one step to the next.

$\phantom{={}}{6\!\left(r+3\right)+8r}$

$={\left(6r+18\right)+8r}$

$={\left(18+6r\right)+8r}$

$={18+\left(6r+8r\right)}$

$={18+\left(6+8\right)r}$

$={18+14r}$

$={14r+18}$

You can earn partial credit on this problem.