Making a proportion helps,
[tex] \frac{2.25 \: mi}{12 \: min} = \frac{x}{60 \: min} [/tex]
[tex] \frac{2.25}{12} \times \frac{5}{5} = \frac{11.25}{60} [/tex]
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Answer : Stephanie can run 11.25 miles in an hour.
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I hope that helps you out!!
Any more questions, please feel free to ask me and I will gladly help you out!!
~Zoey