The shortest side: $600$ ft. The longest side: $1000$ ft. The middle side: $800$ ft.
Work Step by Step
Let the shortest side be $x$ (ft). The longest, then, is $2x-200$, and the middle side is $(2x-200)-200=2x-400$ Their sum (perimeter) is (equals) 2400: $x+(2x-200)+(2x-400)=2400$ $5x-600=2400$ $5x=3000$ $x=600$ The shortest: $600$ ft. The longest = $2(600)-200=1000$ ft The shortest = $2(600)-400=800$ ft.