[Optics Physics] Focal Length Calculation

A tired physics professor can easily read the fine print of the financial page when the newspaper is held at arm's length, 58.5 cm from the eye. What should be the focal length of an eyeglass lens that will allow him to read at the more comfortable distance of 24.5 cm?

I can't seem to find what step i'm missing in solving this even after reading up again on thin lens equations :(