This is College Physics Answers with Shaun Dychko. Magnification is the negative of the focal length of the objective divided by focal length of the eyepiece. So, to find focal length of the eyepiece, we multiply both sides by <i>Fe</i> divided by magnification. And so, we have the focal length of the eyepiece s negative of the objective focal length divided by magnification. So, that's negative of 75 centimeters divided by negative 7.5, which is a 10.0 centimeter focal length for the eyepiece.