I believe the author meant "old.class + old.study = 40" vs "new.class + new.study = 27" (where new.study = 14). It took me a re-read to come to that conclusion.
Ah ok, I see now how this can be read that way. Anyway I question the math. Fulltime enrolment is 15 credits which typically is considered 45h of work a week (1h in-class + 2h studying). What we also shouldn't forget is that on top of that students typically have a job as well.