The volume of a rectangular prism is calculated by multiplying the length, width, and height.
Volume = length x width x height
Volume = (2 1/4) x (1 1/2) x (3/4)
Volume = (9/4) x (3/2) x (3/4)
Volume = (27/8) ft^3
Converting the improper fraction to a mixed fraction:
27 ÷ 8 = 3 with a remainder of 3
Therefore, the volume of the box is 3 3/8 ft^3.