A heavy-duty industrial crane hoist has an efficiency denoted by η\etaη. During operation, the electric motor receives a total power input, PinP_{\text{in}}Pin, and does useful work lifting loads at a rate of PusefulP_{\text{useful}}Puseful.
Write down an equation that expresses η \eta\,η in terms of PinP_{\text{in}}Pin and PusefulP_{\text{useful}}Puseful.