A microscope consists of an objective lens having a focal length of 16.22 mm and an eyepiece having a focal length of around 9.80 mm. With the length of barrel set at 25.0 cm, the diameter of a red blood cells image subtends an angle of around 1.43 mrad with the eye. When the final image distance is around 25.0 cm from the eyepiece, determine the real diameter of the red blood cell?