Two classmates have decided to read all the volumes in a popular series of books. Carly has
already read 10 volumes and will continue to read new ones at a rate of 2 volumes per week.
Lisa, who hasn't started reading the series yet, will read 4 volumes per week. At some point,
Lisa will catch up with Carly and they will be reading the same book. How many volumes will
each girl have read by then? How long will that take?