Packing of Particles in Solids-space Lattices

Technically, this question is from a chemistry course, but I have a question about finding the volume of spheres.

We had to do an experiment with Marshshmallows, plums or anything spherical.

And this is how we learned about three types of packing

-hexagonal closest packing

-face-centred or cubic closest packing

-body-centred packing

One of the things we have to figure out is the density in units/cm^3.

It askes : If a box fit tightly around the three layers, what would its volume be? Assuming a mass of 1 unit per sphere, calculate the density in units/cm^3.

I'm sort of lost when it comes to figuring out the volume and any help you could give me would be greatly appreciated!