An object is kept in front of a concave mirror of focal length 15 cm. The image formed is real and three times the size of the object. Calculate the distance of the object from the mirror.

When an object was kept in front of a concave mirror , its real image was formed in the same place in the same size. If the distance of the object was 20 cm away from the mirror, what would be the distance of the focus of the mirror.