Binding energy in code

You will write three functions that turn atomic masses into binding energies.

The idea. The mass defect is $\Delta m = Zm_H + Nm_n - M$, with atomic masses in u. The binding energy is $B = \Delta m \times 931.494$ MeV. All three functions take the number of protons, the number of neutrons and the atomic mass mass in u.

Your tasks.

1. In mass_defect, return the mass defect in u.
2. In binding_energy, return the binding energy in MeV.
3. In per_nucleon, return the binding energy per nucleon in MeV.