I was able to complete the previous problems thanks to help from here. Here is the final problem set I'm stuck on:

http://imgur.com/SYPzV.jpg

To me it seems that there will always be a positive c so that cg(n) is greater or equal to f(n). No matter how large n is, since there's no limit to how large c can be (can even be a decimal), wouldn't that always be possible?

Thanks.