[tex] \frac{9}{14}\cdot(- \frac{2}{3}) +(- \frac{2}{3}) \cdot \frac{1}{28}+ (- \frac{2}{3}) \cdot \frac{3}{7}= \\ \\ =(- \frac{2}{3}) ( \frac{9}{14}+\frac{1}{28}+\frac{3}{7}) = \\ \\ =(- \frac{2}{3}) ( \frac{9\cdot 2}{14\cdot 2}+\frac{1}{28}+\frac{3\cdot 4}{7\cdot 4})= \\ \\ =(- \frac{2}{3}) ( \frac{18}{28}+\frac{1}{28}+\frac{12}{28})= \\ \\ =(- \frac{2}{3}) ( \frac{18+1+12}{28})=(- \frac{2}{3}) ( \frac{31}{28})= - \frac{2\cdot 31}{3\cdot 28}=-\frac{31}{3\cdot 14}=\boxed{-\frac{31}{42}} \\ \\ R: C.[/tex]
