the distance of a girl from a plane mirror is 15m when she is standing infront of it.she can see her image behind the mirror

1- 15cm
2- 30cm
3- 45cm
4- 10

All you state is "She can see her image".

You have not asked a question, such as "How far away is she from her image?"

If that is what you were meaning to ask, the answer is 30 cm.