If the coefficients of $x^7$ & $x^8$ in the expansion of ${\left[ {2\,\, + \,\,\frac{x}{3}} \right]^n}$ are equal , then the value of $n$ is :

  • A

    $15$

  • B

    $45$

  • C

    $55$

  • D

    $56$

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  • [JEE MAIN 2023]

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