A reversible steady device operates between two thermal reservoirs, one at \(390 \mathrm{~K}\) and one at \(250 \mathrm{~K}\). If no work is done on the device, what is the maximum value for the percentage of thermal energy input \(Q_{\text {in }}\) converted to mechanical energy \(W_{\text {out }}\) ? (Hint: Consider the entropy diagram of a reversible process and the change in entropy.)