The nuclear reaction that powers the sun is the fusion of four protons into a helium nucleus. The process involves several steps, but the net reaction is simply $4 p \rightarrow{ }^{4}$ He $+$ energy. The mass of a helium nucleus is known to be $6.64 \times 10^{-27} \mathrm{kg}$
a. How much energy is released in each fusion?
b. What fraction of the initial rest mass energy is this energy?