If the volume increases by 9 the length dimensions have to increase by ∛9=2.08 approx, but that also increases the height. I suspect that it's the ground area that needs to increase, and the height remains the same. If this is the case then only the length and width have to be increased. This increase is √9=3.
Assuming the height is 2m, then length and width are 4m and 1m. The current volume is 8m3. If the length and width are increased by 3 then they become 12m and 3m, and the total volume is 72m3, which is 9 times 8m3.
If all the dimensions are changed by the same amount, the new dimensions would be 2.08m, 4.16m, 8.32m, resulting in volume 72m3. This would make the height 4.16m which is probably impractical.