Assume that a neutron breaks into a proton and an electron. The energy released during this process is:(Mass of neutron $=1.6725\times 10^{-27}\text{kg}$; mass of proton $=1.6725\times 10^{-27}\text{kg}$; mass of electron $=9\times 10^{-31}\text{kg}$)

The energy released is due to the mass defect $\Delta m$ in the process:
$$\text{n}\to \text{p}+{\text{e}}^{-}$$
The mass defect is:
$$\Delta m=m_n-(m_p+m_e)$$
Given $m_n=1.6725\times 10^{-27}\text{kg}$ and $m_p=1.6725\times 10^{-27}\text{kg}$:
$$\Delta m=1.6725\times 10^{-27}-(1.6725\times 10^{-27}+9\times 10^{-31})$$
Since the proton and neutron masses provided are identical in the question text, the mass defect is effectively the magnitude of the electron's mass:
$$\Delta m=9\times 10^{-31}\text{kg}$$
Energy released $E=\Delta m{c}^2$:
$$E=(9\times 10^{-31})(3\times 10^8{)}^2\text{J}$$
$$E=81\times 10^{-15}\text{J}$$
Converting to $\text{MeV}$ (where $1\text{eV}=1.6\times 10^{-19}\text{J}$):
$$E=\frac{81\times 10^{-15}}{1.6\times 10^{-13}}\text{MeV}\approx 0.73\text{MeV}$$