3/5 of an hour would be 36 minutes (60/5=12, then 12*3=36). If Jerry read for 20 days, then he would read 36*20 minutes in October, so 720 minutes. If we are finding how many hours, we would divide 720/60, which would be 12. That means Jerry read 12 hours in October, and if he read 8 hours in September, then he read 4 more hours in October than September.
