Imagine a corner engine has a hot reservoir of 680k

put in into kelvin  

680+273.15=953.15  

220+273.15=493.15  

953.15-493.15/953.15.  

I got 48% not sure where the rest of these come from.

answer: 802.3 kilo joules of energy represents 191.75 kilo calorie of energy.

explanation:

energy released during combustion of one mole methane = 802.3 kilo joules

if 1 kilo joule = 0.239006   kilo calorie

then ,802.3 kilo joule will be = 802.30.239006 kilo calorie

802.3 kilo joule = 191.75 kilo calorie

hence, the energy in kilo calorie is 191.75 kilo calorie.