The bed of a pickup truck measures 4 feet by 8 feet to the nearest inch, what is the length of the longest thin metal bar that will lie flat in the bed

The bed of the truck is a rectangle, 4-ft wide and 8-ft long.

The diagonal of the rectangle is

                                 √ (4² + 8²)

                             =  √ (16 + 64)

                             =  √ (80)

                             =  8.9442... feet 

                        8.9442... feet =  8 feett  11.33 inches

Rounded to the nearest inch:    8 ft  11 in .   

Are you trying to figure out the volume?