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?
John has to spend 20+40+20 = 
<gadget id="calculator">20+40+20</gadget>
<output>80</output>
80 minutes on homework.
John has 3 hours*60 minutes= 
<gadget id="calculator">3*60</gadget>
<output>180</output>
180 minutes before dinner.
Thus, John has 180-80=
<gadget id="calculator">180-80</gadget>
<output>100</output>
100 minutes for his nap.

<result>100</result>