A forensic pathologist is viewing heart muscle cells with a microscope that has two selectable objectives with

Question:

A forensic pathologist is viewing heart muscle cells with a microscope that has two selectable objectives with refracting powers of 100 and 300 diopters. When he uses the 100-diopter objective, the image of a cell subtends an angle of 3 × 10-3 rad with the eye. What angle is subtended when he uses the 300-diopter objective?