Karyn proofreads 15 pages in 2 hours for $40. what is her proofreading rate in pages per hour?

Hey there,
2 hours = 15 pages
1 hour = 15 / 2
           = 7.5 pages
15 pages = $40
1 page = $40 / 15
            = $2.666666666666667
7.5 pages= $2.666666666666667 x 7.5
               = $20

Hope this helps :))

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What mathematical statement is missing ? ? the answer is b