The diagonal of the figure forms a right angle triangle with the diagonal of the base and the height of the figure.
Diagonal of base = √(3² + 4²)
= 5ft
Diagonal of solid² = Diagonal of base² + height²
height = √((√41)² + 5²)
height = 8.12 feet
Volume = width x length x height
Volume = 3 x 4 x 8.12
= 97.44 cubic feet