Hello,
It's a simple one.
If the object distance (u) is 30 cm and image distance (v) is also 30cm.
So by the formula of a mirror is,
1/f=1/u+1/v u
Puttingall the values,
1/f=1/30+1/30
so,
1/f=1/15
Then,
f=15cm.
Hope you got your answer.
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