Answer:
 9.5 ft wide by 24 ft long
Step-by-step explanation:
A graphing calculator shows there are two solutions to the system of equations ...
 2x + y = 43 . . . . . . fence length when x= width
 xy = 228 . . . . . . .  area
The solutions are ...
 (width, length) = (9.5, 24)  or  (12, 19)
Since we want the length as long as possible, the choice of dimensions is ...
 length = 24 feet; width = 9.5 feet.