Knitting Math

I've lost both my tape measure & my calculator. (I think small hands might have been a cause.)

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Anyways, help me out with this math, ok? If, during the course of this:

(75 min)

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I can get this done...

(Approx 5 inches.) (Blurred for discretion. Color is true though, and doesn't cover the luscious, luscious texture of cashmere/silk.)

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How long is it going to take me to knit another, erm, 28 inches or so?

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Or should I be wondering if I'll be able to recite Merriweather's lines in my sleep?