Start like this: Let $\langle S,* \rangle$ be isomorphic to $\langle T, \Box\rangle$. Assume $\langle S,* \rangle$ is commutative. I claim that $\langle T, \Box\rangle$ is commutative. To prove this, let $a,b \in T$. ... **continue computation to get**... $a\Box b = b \Box a$. Therefore ....