I was going through sample questions for Science Olympiad, and one of the questions went like this:
A cell is observed through a light microscope at 4x magnification. The cell takes up about half of the visual field. What is the approximate length of this organism?
I know from prior knowledge that a cell can be anywhere from $10$ to $100$ micrometers, but I don't know how to figure out a cell's size with the information I'm given. Usually when I do problems like this, I am given the size of the field of view. Is that not needed to solve this problem?