Calculating enthalpy of formation of ethane from combustion data

[nevada2012]

hey guys i am having a really hard time doing enthalpy problems,

i am trying to do this(its not an homework question)


Calculate the enthalpy of formation of ethane (C2H6) given that the enthalpy of combustion of ethane is
-2840kj. DeltaHfH2O(1) = -286 kg/mol Delta HfCO2 (g) =-394 kg/per

is the answer -206?

this is what i did

-286 X -2840/-394


if not can you please give me step by step

 

[Zeppos10]

shouln't you first write out the reaction-equation ??
I wonder which textbook you are using ??