In order to produce an inverted image of a real object that is exactly the same size as the object using only a spherical mirror, how far from the

In order to produce an inverted image of a real object that is exactly the same size as the object using only a spherical mirror, how far from the mirror should the object be placed ( f is the focal length of the mirror)?

The correct answer is 2f, can you please explain why that is the correct answer ?

Thanks!