1. The problem statement, all variables and given/known data Humankind uses about 500 EJ of energy each year nearly all of it from fossil fuels. If the energy content of fossil fuels is 40 MJ/kg estimate the total mass of fossil fuels we burn each year. 2. Relevant equations I am not sure if this is a relevant equation but in my text book there is a similar example showing the energy content of divided by the total thermal power extracted measured in MJ/kg 3. The attempt at a solution I really don't know if I'm doing any of this right but I thought I needed to convert the 500 EJ into MJ. I got 5 x 10^14. This problem is talking about a year while the text book shows per second. Do I need to convert to seconds in a year? If so i got 31, 536,000 seconds. Not sure if I even needed to do this... I have no idea if I even started this problem right or where to go from here if I have?