Volume of a pyramid (V) = 1/3 x area of the base x height
Area of the base = area of a square = lenght^2
Perimeter of the base = lenght x 4 = 18.1
4 L = 18.1
Solve for L
L = 18.1 /4
L = 4.525
Area = 4.525 ^2 = 20.48 ft2
Back with the volume formula:
V = 1/3 x 20.48 x 28.1 = 191.83 ft3