The mass of the sun is 2*10^30 kg. it currently consists to about 70% (mass) of hydrogen. the dominant source of energy for the sun is the pp-chain (type i) fusion process in which four protons fuse into a 4he core consisting of two protons and two neutrons. this process releases 26.22 mev ( = 4.2*10^-12 j) of energy. assume that to first order the luminosity of the sun remains constant at 1.1 times its current-day value. how long will it take for the sun until the fraction of hydrogen is reduced from 70% to 30%?