Combustion of paraffin
The question is ambiguous, unfortunately.  There are two possibilities that I can see.  Either the question:


is asking about a reaction in which some quantity of wax undergoes the reaction you give, in which case you are 100% correct.
is asking about a reaction in which part of the paraffin is being oxidized to C and part is being oxidized to CO2, the usual reaction that occurs.  Though that is more likely to occur in real life, in my opinion, it also is impossible to solve without further information.  The best you could do would be to set a lower limit (the value you've already found) and an upper limit, the heat of reaction for $\ce{C21H44 + 32 O2 -&gt; 21 CO2 + 22H2O}$.  (I guess that would be an upper limit and a lower, numerically, since the values are both negative, but this reaction would release far more heat.)