Use the value of the Sun's luminosity (3.90×1026 watts, or 3.90×1026 joules per second) to calculate what mass of hydrogen the Sun will convert into helium during its entire main-sequence lifetime of 1.2×1010 years. (Assume that the Sun's luminosity remains nearly constant during the entire 1.2×1010 years.) What fraction does this represent of the total mass of hydrogen that was originally in the Sun?