36
Read more: http://wiki.answers.com/All_the_multiples_of_6_from_1_to_100#ixzz1LhkAON2t6,12,18,24,30,36,42,48. . .
1x62x3
6 12 18 24 30 36 42 48 54 60 66 72 78 84 90 96
Volume of a box = lbh= Length x Breadth x Height = 6 x 6 x 6 = 216m³ assuming the dimensions you gave were in meters