Tony exercises every morning by walking 3 miles carrying a 25-pound backpack, then he runs another 10 miles without the backpack.  If he walks at a speed of 3 miles per hour and runs at a speed of 5 miles per hour, how many hours each week does he spend exercising?
Tony walks 3 miles at 3 miles per hour for 3/3=1 hour.
Tony also runs 10 miles at 5 miles per hour for 10/5=
<gadget id="calculator">10/5</gadget>
<output>2</output>
2 hours.
Thus, each day he exercises for 1+2=
<gadget id="calculator">3</gadget>
<output>3</output>
3 hours.
Over the course of one week, he exercises for 3*7=
<gadget id="calculator">3*7</gadget>
<output>21</output>
21 hours.

<result>21</result>