How do the number of protons neutrons and the mass number relate to each other?

Mass number:

The element's mass number is nothing but the sum of total number of neutrons and protons present in the element's nucleus. For example, if the mass number of nitrogen is 14, it means that there are 7 number of protons and 7 number of neutrons in the nucleus of the nitrogen.

The relationship between the number of proton and the neutron with that of mass number is that, the latter gives the count of the former. On contrary, the atomic number denotes the weight of the atom.

Mass number = protons + neutrons

If you have the # of protons and the mass #, subtract the number of protons from the mass number to get the number of neutrons.

If you have the number of neutrons and the mass number, subtract the number of neutrons from the mass number to get the number of protons.