What is the distance between the image and the plane mirror, if the object is at $15\;m$?

Hint: We know that the plane mirror is a flat mirror which reflects the incident light falling on it. Also, the angle of incidence of the incident angle is equal to the angle of reflecting angle in a plane mirror. Using the given and the property of a plane mirror we can solve the question as shown below.

Complete step by step solution:
We know that a mirror reflects or bounces back, only a fraction of the beam of light in a single direction, as compared to other objects which either scatter light or absorb it. They are used to see one's reflection, like the normal mirror we use in the house, or are used to see objects that are not visible directly, like rear mirrors and dentist’s mirrors. There are various types of mirrors on the basis of shapes, like plane mirrors , the ones we use generally, which provide real images and curved mirrors, which may distort or magnify the image, generally seen in mirror mazes.
Let us look at the following properties of a plane mirror, when an object is placed at a distance y from the mirror, the reflection of the object looks like it is y distance into the mirror. Thus the total distance between the image and the object will be $2\;y$.
Given that the distance between the object and the mirror $y=15m$, then the distance between the image and the object will be $2\;y=2\times 15=30\;m$
Thus the distance between the image and the object will be $30\;m$

Note: This is a very simple question. It only involves the understanding of the relative distances between the object and distance. Also using the property of plane mirrors we can solve the question very easily. Mirror reflects or bounces back, only a fraction of the beam of light in a single direction. Be careful with the sign conventions used. Also note that the focal length is half the radius of curvature of the spherical mirror.