The earth and the moon are assumed to be spheres.
The volume of a sphere is given by the formula V= 4/3 (πr^3), where r is the radius of the sphere.
Note that the radius is 1/2 the diameter.
So the radius of the earth is 3960 miles (this is 7920/2)
And the radius of the moon is 1080 miles (this is 2160/2)
We can now solve for the volumes of the earth and the moon by using the formula.
For earth, V=4/3 (π x 3960^3) which is equal to 2.6 x 10^11 cubic miles.
For the moon, V=4/3 (π x 1080^3) which is equal to 5.3 x 10^9 cubic miles.
This means that the earth has a larger volume than the moon and is generally larger in size.