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 = <<900/9=100>>100 seconds
Then find the time it takes Jill to run down the hill: 900 feet / 12 feet/second = <<900/12=75>>75 seconds
Then add the two times to find Jill's total time: 100 seconds + 75 seconds = <<100+75=175>>175 seconds
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