A boxer delivers a hard blow to the chin of his opponent. The inertia of the boxer$$s hand $($with glove$)$ and forearm is $3\mathrm{.}0$ kg$,$ and the inertia of the opponent$$s head is $6\mathrm{.}5$ kg$.$ You learned in neurobiology class about $10$ J of extra internal energy will render an opponent wobbly$-$kneed, and you guess that about half of the converted energy will end up in the opponent$$s head. Assuming a coefficient of restitution e$=0\mathrm{.}20,$ with what speed does the boxer$$s fist have to contact the opponent$$s head in order to deliver the punch?