Jill can run up a hill at 9 feet/second and down a hill at 12 feet/second. How long does it take her to run up and down a 900 foot hill?
First find the time it takes Jill to run up the hill: 900 feet / 9 feet/second = 
<gadget id="calculator">900/9</gadget>
<output>100</output>
100 seconds.
Then find the time it takes Jill to run down the hill: 900 feet / 12 feet/second = 
<gadget id="calculator">900/12</gadget>
<output>75</output>
75 seconds.
Then add the two times to find Jill's total time: 100 seconds + 75 seconds = 
<gadget id="calculator">100+75</gadget>
<output>175</output>
175 seconds.

<result>175</result>