Cube a to cube b is 1:3. This is a one-to-one measure. If we want volume ratios, we have to take the one-to-one ratios and cube them. Like this: which simplifies to . This means that the volume of the smaller object is 27 times smaller than the volume of the larger.
Volume of a sphere = (4/3) pi r^3
required volume = (4/3) pi (6^3-5^3)
= (364/3) * pi cu ins.
64%. Not a random number. I did it with this tool I programmed on my own, but BE WARNED it is still buggy so this answer might not be correct. I will send the tool when it's 100% done if you want :)