Answer: The correct option is
(D)
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Step-by-step explanation: We are given to solve the following inequality for the unknown variable n :

To solve the given inequality for n, we must take terms involving n on the left side and other terms on the right side of the inequality.
From inequality (i), we have
![21k-3n+9p>3p+12\\\\\Rightarrow -3n>3p+12-21k-9p\\\\\Rightarrow -3n>-6p-21k+12\\\\\Rightarrow 3n<6p+21k-12~~~~~~~~~~~~~~~~~[\textup{since }a>b~~\Rightarrow -a<-b]\\\\\Rightarrow n<(6p+21k-12)/(3)\\\\\Rightarrow n<2p+7k-4.](https://img.qammunity.org/2019/formulas/mathematics/middle-school/tgbmrm71jh5ge3csv31sow6bkm1zg8jol5.png)
Thus, the required solution for n is
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Option (D) is CORRECT.