24 by 72 by 18 in cubic feet

I have to assume that the 24, the 72, and the 18 are feet.

If those are the dimensions of a rectangular prism, like a box, a crate,
or a humongous block of ice, then

            Volume = (length) x (width) x (height) =

                             (24-ft) x (72-ft) x (18-ft) =  31,104 cubic ft

If those numbers are inches, then here's the easy way to handle it:

       24 inches  =  2 ft
       72 inches  =  6 ft
       18 inches  =  1.5 ft

               Volume  =  (length) x (width) x (height) =

                                     (2ft) x (6ft) x (1.5ft)  =  18 cubic feet

What do you mean i don’t understand