Answer
$$W = 47,520,000{\text{ ft - lb}}$$
Work Step by Step
$$\eqalign{
& {\text{From the information we have:}} \cr
& F = {\text{9tons }}\left( {{\text{force}}} \right) \cr
& D = \frac{1}{2}{\text{mile }}\left( {{\text{distance}}} \right) \cr
& {\text{Unit conversions}} \cr
& {\text{9ton}}\left( {\frac{{2000{\text{lb}}}}{{1{\text{ton}}}}} \right) = 18,000{\text{lb}} \cr
& \frac{1}{2}{\text{mile}}\left( {\frac{{5280{\text{ft}}}}{{1{\text{mile}}}}} \right) = 2,640{\text{ft}} \cr
& {\text{Using the Definition of Work Done by a Constant Force}} \cr
& W = FD{\text{, Work}} = \left( {{\text{force}}} \right)\left( {{\text{distance}}} \right) \cr
& {\text{Substituting the known values}} \cr
& W = \left( {18,000{\text{lb}}} \right)\left( {2,640{\text{ft}}} \right) \cr
& W = 47,520,000{\text{ ft - lb}} \cr} $$
