Explanation
This problem describes an inclined plane and, for an inclined plane, the effort force multiplied by the effort distance equals the resistance force multipied by the resistance distance:
\(F_{e} d_{e}=F_{r} d_{r}\)
Plugging in the variables from this problem yields:
\(F_{e} \times 20 \mathrm{ft}=280 \mathrm{lbs} .4 \mathrm{ft} .\)
\(F_{e}=1120 f t . l b s . / 20 f t=56 l b s .\)