Draw a picture if you have a hard time imagining what this flattened box looks like. The height of the box when folded up will be 6ft. The length and width will both be x. Volume is then ..
v = 6x²
use the volume given (864 ft³) to find the length/width of the box.
864 = 6x²
864/6 = x²
144 = x²
12 = x
The question asks for the length of the sheet used to make the box.Add the 6 ft square lengths to find this. See the picture I made.
S = x + 12
S = 12 + 12
S =24 ft