A student was asked to find the arithmetic mean of the numbers $3,11,7,9,15,13,8,19,17,21,14$ and $x$. He found the mean to be $12 .$ What should be the number in place of $x ?$

  • A

    $3$

  • B

    $7$

  • C

    $17$

  • D

    $31$

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