i need to build a box that equals .78 cu ft any ideas on how i do this

The volume of a box is its length times its width times its height so to construct a box with a volume of 0.78 cubic feet you need three numbers, length, width and height so that

length width height = 0.87

So, for example you could construct a box with length 1 foot, width 1 foot and height 0.87 feet. Another possibility is a box that has length 2 feet, width 1 foot and height 0.435 feet.

Penny