Compute all parts of given problem:
Problem: A slide projector needs to create a 87 cm high image of a 2.0 cm tall slide. The screen is 310 cm from the slide. Assume that it is a thin lens.
Part A: What focal length does the lens need?
cm
Part B: How far should you place the lens from the slide?
cm
Please do a step by step solution since I'm kind of lost with this problem.