A shortsighted person consists of a far point which is 4.2 m from his eye. Determine what focal length lenses he must use in his contact lenses to let him to focus on distant objects. Please illustrate computations and pick the best answer from under.
i) -4.2m
ii) 4.2m
iii) -5.2m
iv) 5.2m
v) 4.8m