Find the density of neutron star by finding its volume using the radius

Neutron stars are believed to be composed of solid nuclear matter, primarily neutrons.     a. If the radius of a neutron is 1.0 x 10^-13 cm, calculate the density of a neutron in g/cm^3. (volume of a sphere=4/3 pi r^3)   b. Assuming that a neutron star has the same density as a neutron, calculate the mass in kilograms of a small piece of a neutron star the size of a spherical pebble with a radius of 0.10mm.

radius is given to you and volume = 4/3 pi r^3

use the given radius to find volume and then mass of neutron star to find density

density = mass / volume