It takes Derek 9 minutes to walk a mile if he doesn't have to walk with his brother. If he has to take his brother it takes 12 minutes to walk a mile. How many minutes longer would it take him to walk 20 miles if he had to take his brother?
Alone it would take him 9*20=
<gadget id="calculator">9*20</gadget>
<output>180</output>
180 minutes.
With his brother, it would take him 12*20=
<gadget id="calculator">12*20</gadget>
<output>240</output>
240 minutes
240-180=
<gadget id="calculator">240-180</gadget>
<output>60</output>
60 more minutes.

<result>60</result>