Solve the Problem $x$ Feet Long, Express the Area of the Dog Run as Dog

Solve the problem.
-Elissa wants to set up a rectangular dog run in her backyard. She has 24 feet of fencing to work with and wants to use it all. If the dog run is to be $x$ feet long, express the area of the dog run as a function of $x$ .

A) $A ( x ) = 11 x - x ^ { 2 }$
B) $\mathrm { A } ( \mathrm { x } ) = 13 \mathrm { x } - \mathrm { x } ^ { 2 }$
C) $\mathrm { A } ( \mathrm { x } ) = 14 \mathrm { x } ^ { 2 } - \mathrm { x }$
D) $A ( x ) = 12 x - x ^ { 2 }$