Solve the Problem $F = k / x ^ { 2 }$

Multiple Choice

Solve the problem.
-The gravitational force (in lb) of attraction between two objects is given by $F = k / x ^ { 2 }$ , where $x$ is the distance between the objects. If the objects are $5 \mathrm { ft }$ apart, find the work required to separate them until they are $50 \mathrm { ft }$ apart. Express the result in terms of $k$ .

A) $\frac { 1 } { 10 } \mathrm { k }$
B) $\frac { 1 } { 250 } \mathrm { k }$
C) $\frac { 1 } { 45 } \mathrm { k }$
D) $\frac { 9 } { 50 } \mathrm { k }$