The sun radiates energy at the rate $3.8 \times 10^{26}$ W. The source of this energy is fusion, a nuclear reaction in which mass is transformed into energy. The mass of the sun is $2.0 \times 10^{30} \mathrm{kg}$
a. How much mass does the sun lose each year?
b. What percentage is this of the sun"s total mass?
c. Estimate the lifetime of the sun.