The tennis balls' box

        Tennis balls can be sold in cylinder-shaped boxes of four with interior diameter 7 cm and height 26.8 cm. Each ball has a diameter of 65 mm.  

What is the interior volume of the box in cm³?
cm³

What is the volume of a ball in cm³? cm³

What is the volume of the empty space, in cm³,
when the four balls are in the box?
cm³