Sixty-three joules of heat are added to a closed system. The initial internal energy of the system is 58 J, and the final internal energy is 93 J.

The change in internal energy is 93 J − 58 J = 35 J. Using the first law, ΔU = Q − W, where W is the work done by the system, gives W = 63 J − 35 J = 28 J. The correct choice is 28 J.

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