How do I specify gutter margins on a Pages document?

I have a MacBook Air. I'm preparing a 7" x 10" book to submit to Create Space. I must create the document "print ready" and must specify all margins, top, bottom, inside and outside, as well as gutter margins. I also must specify that there should be "Mirror Margins" on all pages. I have specified the top and bottom margins on the Document page, but I have found nowhere to specify gutter and mirror margins. Does anyone know how to solve this problem? Thanks!