Q:  How many kg of gasoline would the
      Sun have to burn each second to
      produce its current luminosity?


         The rate of fuel use would be

 
                      luminosity (J/s) 
           rate  =   ------------------
                      energy per kg


                      3.9 x 10^(26) J/s
                 =   ------------------  
                        45 x 10^6 J/kg


                 =   8.7 x 10^(18)  kg/s