question: 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?
answer: John has to spend 20+40+20 = <<20+40+20=80>>80 minutes on homework.
  John has 3 hours*60 minutes= <<3*60=180>>180 minutes before dinner.
  Thus, John has 180-80=<<180-80=100>>100 minutes for his nap.
  #### 100