Physics

Problem

A student places a small object

30\,\text{cm}

in front of a thin convex lens. The real image forms

45\,\text{cm}

on the opposite side of the lens. What is the focal length of the lens, to the nearest whole centimeter? a)

15\,\text{cm}

75\,\text{cm}

18\,\text{cm}

24\,\text{cm}