The Focal Length of the Lens of a Simple Film

Multiple Choice

The focal length of the lens of a simple film camera is 40.0 mm.By what amount should the distance between the lens and the film be increased or decreased to change the focus from a person who is 25 m from the lens to one who is 4.0 m from the lens?

A) 0.2 mm
B) 0.3 mm
C) 0.4 mm
D) 0.5 mm
E) 0.7 mm