(a) 24 cm in front of mirror

(b) 36 cm in front of mirror

(c) 48 cm in front of mirror

(d) (a) and (b)

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$\large\frac{1}{v}+\frac{1}{u}=\frac{1}{f}$

or $\large\frac{u}{v}$$+1=\frac{u}{f}$

Since $m =\large\frac{-v}{u}$

$\therefore m= \large\frac{f}{f-u}$

Here $f= -30\;cm$ and $m=\pm 5$ because image can be real or virtual .

for real image $m=-5$

$\therefore -5= \large\frac{-30}{-30 -u}$

or $u= -36 \;cm$

for virtual image $m=+5$

$\therefore 5=\large\frac{-30}{-30-u}$

or $u= -24 \;cm$

Hence the object must be placed at 24 cm or 36 cm in front of concave mirror.

Hence d is the correct answer.

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