A pair of glasses is designed for a person with a far-point distance of 3 m so that she can read street signs 17.5 m awa

[answerhappygod]

A pair of glasses is designed for a person with a far-point
distance of 3 m so that she can read street signs 17.5 m away. (The
far-point distance is the distance from the eye at which you are
just able to properly focus a distant object.)
(a) If the glasses are to be worn 1.0 cm from her eyes, what is
the needed focal length?
(b) Compare this focal length (find the percent difference) to
the focal length she would need if she chooses a style of glasses
that fit on her face so that the lenses are instead 2.0 cm away
from her eyes.