(c) Magnetic field at $P$ due to $PQ\ \&\ PR$ is zero
$\therefore$ Magnetic field at $P$ due to $QR$
$B = \frac{\mu_{0}}{4\pi} \bullet \frac{I}{PS}\left( \sin\alpha + \sin\beta \right)$
Where, $B = \frac{\mu_{0}}{4\pi} \bullet \frac{1}{\frac{12x}{5}}\left\lbrack \frac{3}{5} + \frac{4}{5} \right\rbrack$
$B = \frac{\mu_{0}}{4\pi} \times \frac{1}{12x} \times 7 = \frac{7\mu_{0}I}{48\ \pi x}\ \therefore k = 7$
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