Standard Enthalpy of Combustion

[Lauryn Shinno 2H]

For 8.57 in the 6th edition, it gives us the standard enthalpies of combustion. In the solution manual, it writes balanced combustion equations for the given reaction and then adds the reactions together to find the final enthalpy. Do we need to do this? I literally added the given enthalpies of combustion together (except I multiplied the enthalpy of the molecule that was formed by -1 to make it positive) and got the same answer.

[Andrea Zheng 1H]

I think the solution manual is just giving a visual way of explaining what you did in your head. It is just showing how the combustion reactions cancel out to form the equation given in the exercise and why you would flip the sign for Hc of C2H6. I don't think you would necessarily need to show all these steps, as you still ended up with the same answer, but I think it's just a way to keep track of the steps when reactions get more complicated. You would probably just need to explain how you got your answer.