A picture is described with different images in it. One of those images is a spherical mirror. This means that the mirror is shaped like a sphere or round object. The term concave refers to the shape of it where it is curved. The focal length is twenty centimeters, but that refers to the amount of light that converges and it is the length of it.
If something is placed in this picture that is ten centimeters from the mirror and it is in front of it, it is on the mirror’s axis. This means that this is the line of rotation. The object would be twenty centimeters behind the mirror based on the placement of the object and the measurements that also are given.