Chemical energetics: explain question

The standard enthalpy change for the formation of ethane, $\ce{C2H6(g)}$, from its elements cannot be measured directly because the reaction is slow and incomplete. The standard enthalpy changes of combustion of carbon, $\ce{C(s)}$, hydrogen, $\ce{H2(g)}$, and ethane, $\ce{C2H6(g)}$, are all known. Explain how Hess's law can be applied to determine the standard enthalpy change of formation of ethane using these data. Include in your explanation the structure of the energy cycle and how the known enthalpy changes are combined.