Combining enthalpy equations to find combustion of magnesium

[intellekt]

Hi, I am stuck on this one question for a lab analysis I am doing. I missed the class where the teacher explained this and a lot more stuff. I also recall a question like this on a test I wrote on friday

Anyway here it is:

Algebraically combine equations (2), (3), and (4) and their corresponding [Change in Enthalpy] values, to get (1) and [Change in Enthalpy] of combustion of magnesium.

I just need to know how to do it, I can plug in the values after right?

Let me know! thanks in advance!

 

[siddharth]

Have you learned about Hess's Law?
"[URL
Your question requires a direct application of Hess's Law.

 

[intellekt]

Ya I have learned Hess' law but I'm still unsure...

So do I change the signs then add them together to get the enthalpy of equation 1?