\begin{aligned}
\mathrm{E} &=\frac{\text { Workdone by load }}{\text { Workdone by effort }} \times 100 \% \\
&=\frac{\text { Load } \times \text { Load distance }}{\text { Workdone by effort }} \times 100 \% \\
&=\frac{(640 \times 1) \mathrm{J}}{8001} \times 100 \% \\
&=80 \%
\end{aligned}