Let $f$ be a function satisfying $f(xy) = \frac{f(x)}{y}$ for all positive real numbers $x$ and $y.$ If $ f(30) = 20,$ then the value of $f(40)$ is-

  • A

    $15$

  • B

    $20$

  • C

    $40$

  • D

    $60$

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