The radiation flux from the sun at the top of the earth's atmosphere is 0.139 J cm-2 s-1 at normal incidence. The earth is 1.50x108 km from the sun. Calculate: (a) the energy production in the sun in MeV/s (b) the rate of hydrogen consumption in g/s (c) how long hydrogen-burning can continue in the sun under the assumption that energy production continues at the present rate and that hydrogen burning will cease when 10% of the total hydrogen mass has been used up. The mass of the sun is 2.0x1033g. I have determined that the energy production in the sun is 2.5e39 MeV/s by converting the flux to MeV/cm^2*s and multiplying that by the area of the sphere produced by the radiation with r=1.50x108 km. However, I'm not sure how to calculate b & c. I was thinking it may have to do with the pp1 chain?