(A) Diagonal $= \sqrt{2}\times side=5 feet \\ \implies side = \frac{5}{\sqrt{2}} feet$
Parameter $=4\times side = 4 \times \frac{5}{\sqrt{2}} = 10\sqrt{2} feet = 14.142 feet$
(B) $a=3 feet, b=4 feet $
Parameter $=2\times(a+b) = 2\times(3+4) = 2\times 7 = 14 feet$
(C) $side =48 inches = \frac{48}{12} = 4 feet$
Parameter $ =3\times side = 3\times 4 = 12 feet $
(D) longest diagonal $=2\times side = 6 feet \\ \implies side = 3 feet$
Parameter $= 6\times side = 6 \times 3 = 18 feet $
Option D is correct.