Explanation
Due to friction, a machine will never be able to utilize 100% of its work input. A certain percentage of that input will be lost in overcoming friction within the machine.
\(\text { Efficiency }=\frac{\text { Work }_{\text {out }}}{\text { Work }_{\text {in }}} \times 100=\frac{39 f t . l b .}{130 f t . l b .} \times 100=30 \%\)