Sam purchases +3.50-diopter eyeglasses which correct his faulty vision to put his near point at 25 cm.

Question:

Sam purchases +3.50-diopter eyeglasses which correct his faulty vision to put his near point at 25 cm. (assume he wears the lenses 2.0 cm from his eyes.)
(a) Calculate the focal length of Sam’s glasses.
(b) Calculate Sam’s near point without glasses.
(c) Pam, who has normal eyes with near point at 25 cm, puts on Sam’s glasses, calculate Pam’s near point with Sam’s glasses on.