4 kilograms equals how many cubic feet?

Answer 1

This question cannot be answered sensibly. A cubic foot is a measure of volume, with dimensions [L3]. A kilogram is a measure of mass, with dimensions [M]. Basic dimensional analysis teaches that you cannot convert between measures with different dimensions such as these without additional information. It takes only a little mental effort to compare a cubic foot of air and a cubic foot of lead to see that the two will have very different masses.