A compound microscope has the objective and eyepiece mounted in a tube that is 15.0cm long. The focal length of the eyepiece is 2.72cm , and the near-point distance of the person using the microscope is 25.0 cm.
If the person can view the image produced by the microscope with a completely relaxed eye, and the magnification is -4825, what is the focal length of the objective? (mm)