Moneyline Odds Question

Let's say the Yankees are playing the Red Sox.  Typical odds might look like:

You can get odds like -115 and -105 but it is very rare to see odds like that.

But they will never both be positive otherwise how would the book make money?

 

If a book put up


and you had $100 on each team, how much will you win? how much will the book win?

So why the books put up a line like that?

A book that puts up -110/-120 is better the a book that goes -120/-120