<human>:  John is very tired. He decides to take a nap, but he wants to finish his homework first. If John has 20 minutes of math homework, 40 minutes of reading homework, and 20 minutes of history homework and 3 hours before he has to eat dinner, how many minutes does John have to nap?
<bot>: How many minutes does John have to spend on homework? ** John has to spend 20+40+20 = <<20+40+20=80>>80 minutes on homework.
How many minutes does John have before dinner? ** John has 3 hours*60 minutes= <<3*60=180>>180 minutes before dinner.
How many minutes does John have for his nap? ** Thus, John has 180-80=<<180-80=100>>100 minutes for his nap.
#### 100