$\frac{3}{7}.15\frac{1}{3}+\frac{3}{7}.5\frac{2}{5}\le x\le \left( 3\frac{1}{2}:7-6\frac{1}{2} \right)\left( -2\frac{1}{3} \right)$

$\frac{3}{7}.\frac{46}{3}+\frac{3}{7}.\frac{27}{5}\le x\le \left( \frac{7}{2}.\frac{1}{7}-\frac{13}{2} \right).\left( -\frac{7}{3} \right)$

$\frac{311}{35}\le x\le 14$

8$\frac{31}{35}$ $\le x\le $ 14

x $\in $ {9; 10; 11; 12; 13; 14}

Vậy đáp án đúng là: D.