Your roommate Chris leaves some eyeglasses on a table and you, a curious PHYS 251 optics student, take a look through them. You look at an object that is 156 cm away from the lens and from parallax you judge its upright image to be 45 cm away. From this you estimate Chris' prescription to be ____ D. (Answer in D to the nearest 0.05 D, and neglect the space between the eye and corrective lens.)