If an object is placed at a distance of 7.5 cm from a plane mirror, how far would it be from its image?

The object would be 15cm far away from its image if it is placed at a distance of 7.5cm from the plane mirror.

The object is at 7.5cm from the mirror, then the image of the object is 7.5cm on the other side of the mirror. Hence, the image is a total of 15cm from object (7.5cm to the mirror+ 7.5cm to the image).