A microscope has an objective lens with a focal length of 16.22 mm and an eyepiece with a focal length of 9.72 mm. With the length of the barrel set at 28.0 cm, the diameter of a red blood cell's image subtends an angle of 1.43 mrad with the eye. If the final image distance is 28.0 cm from the eyepiece, what is the actual diameter of the red blood cell? Hint: To solve this equation, go back to basics and use the thin-lens equation.