w = number of weeks
b(w) = number of books read after w weeks
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b(w) = 12 translates to "after w weeks, Katy will have read 12 books" or put another way "Katy will have read 12 books after w weeks". The 'w' is a placeholder for some number
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b(2) = 10 means "Katy has read 10 books after 2 weeks". We use the same basic idea talked about above, but we replace w with 2. At the same time, we use 10 instead of 12.
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b(3) = f means "Katy has read f books after 3 weeks" or "after 3 weeks, Katy has read f books". Like w, the f is a placeholder for some number.
