Two classmates have decided to read all the volumes in a popular series of books. Zoe has already read 12 volumes and will continue to read new ones at a rate of 2 volumes per week. Ella, who hasn't started reading the series yet, will read 3 volumes per week. At some point, Ella will catch up with Zoe and they will be reading the same book. How many volumes will each girl have read by then? How long will that take?