Question

A small sample of coal, when completely converted into energy, releases 3.75 * 10 ^ 34j What is the initial mass of coal, assuming the final mass is 0? 

Answer 1

 Coal has a specific heating value

$$2.9\times 10^7J/kg$$

If the final mass is taken as 0, then we get

$$\frac{3.75\times 10^{34}}{2.9\times 10^7}=1.29\times 10^{28} kg$$