6. Using several computers to input a book manuscript simultaneously, it is planned to be completed in several hours. If 3 more computers are added, it will only take $75 \%$ of the original time. If 3 fewer computers are used, it will take more hours than the original time. Then, the originally planned time to complete the input of this book manuscript is ( ) hours.
(A) $\frac{5}{3}$
(B) $\frac{10}{3}$
(C) $\frac{5}{6}$
(D) $\frac{11}{6}$
Analysis: The total workload remains unchanged, the ratio of the number of computers is the inverse of the speed ratio. Let the original number of computers be $\mathrm{x}$, $\frac{x}{x+3}=\frac{75 \% \times 1}{1}=-\frac{1}{4}$, solving this gives $\mathrm{x}=9$. Let the original planned time be $\mathrm{y}$, according to the problem, we have: $\frac{9}{9-3}=\frac{y+\frac{5}{6}}{y}$, solving this gives $\mathrm{y}=\frac{5}{3}$.