So we found some books from 1907 and were wondering how much they were worth.?

There's no way to answer this. It depends upon the edition, how rare it is, how much demand there is and a host of other factors. Your best bet is to find a dealer who specializes in old books and get them appraised. Keep in mind that old books aren't necessarily valuable. Today I picked up a hardback printed in 1998 for less than $1.