The total volume of the baseballs (radius 3.1 cm) can be found by multiplying the volume of one baseball (4/3)*pi*r^3 by 12:
(4/3) * pi * r^3 = (4/3)*3.14159* (3.1)^3 = (4/3)*3.14159*29.791 = 124.788 cu cm for one ball
The volume of 12 of these would be 124.788*12 = 1497.46 cu cm
possible dimensions:
1 row of 12 balls: 74.4 cm (6.2*12) by 6.2 cm by 6.2 cm=2859.936 cu cm ; airspace in box = total box volume-total baseball volume=2859.936 cu cm -1497.46 cu cm= 1362.476 cu cm
2 rows of 6 balls: 12.4 cm (6.2*6) by 37.2 cm (6.2*6) by 6.2 cm=2859.936 cu cm ; airspace in box = total box volume-total baseball volume=2859.936 cu cm -1497.46 cu cm= 1362.476 cu cm
3 rows of 4 balls: 24.8 cm (6.2*4) by 18.6 cm (6.2*3) by 6.2 cm=2859.936 cu cm; airspace in box = total box volume-total baseball volume=2859.936 cu cm -1497.46 cu cm= 1362.476 cu cm
2 levels of 2 rows of 3 balls: 12.4 cm (6.2*2) by 18.6 cm (6.2*3) by 12.4 cm (6.2*2) = 2859.936 cu cm; airspace in box = total box volume-total baseball volume=2859.936 cu cm -1497.46 cu cm= 1362.476 cu cm
I hope this helps....