Understanding Bond Enthalpies: Make and Break Bonds

[Beeorz]

Bond Enthalpies..please help!

Got the first one, but can't figure out how to do "b" and "c." Not understand which ones make/break.

http://rapidshare.com/files/157266091/Enth.jpg

 

[Borek]

If you don't see it, try brute force approach - list all bonds before reaction and after reaction.