Vision Problems: Without glasses, a person can comfortably read a magazine when it is held at 60 cm from his eyes. What should be the focal length of his contact lenses to allow him to read the magazine comfortably at a distance of 30 cm?
A. -30 cm
B. +30 cm
C. -60 cm
D. +60 cm
E. +90 cm
Answer: D
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