C is four times more efficient as a worker than D, which allows C to complete a work in 45 days less than D. If they work together, they can finish the work in:

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Accepted Answer

1. Let D take $x$ days. C is 4 times as efficient, so C takes $x/4$ days.
2. Given C finishes 45 days less: $x-45= x/4$. Solve: $4x-180=x$, so $3x=180$ and $x=60$.
3. So D = $60$ days and C = $15$ days.
4. Together rate = $1/60+1/15=1/60+4/60=5/60=1/12$. Time = $12$ days.

FINAL_ANSWER: b

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