1. The problem statement, all variables and given/known data A student is reading a lecture written on a blackboard. Contact lenses in her eyes have a refractive power of 57.50 diopters; the lens-to-retina distance is 1.750 cm. (a) How far (in meters) is the blackboard from her eyes? (b) If the writing on the blackboard is 5.00 cm high, what is the size of the image on her retina? 2. Relevant equations 1/f = 1/di + 1/do 3. The attempt at a solution (a) I know that once you get f (meters) using the given diopters measurement, you can use that to get an image. f = .0174 m...and then i get di = 0.328 m. (b) i substract 5 cm from 1.75 cm to get object distance...then i use f = .0174 m...finally, i plug in the equation and get di = 27 m. I am not sure if I did this right because the negative and positive stuff really bother me. anyways, help me out if you see something wrong and let me know if i "might" right too! thanks.