Question

A 2.5 cm-tall object stands in front of a converging lens. It is desired that a virtual image 2.2 times larger than the object be formed by the lens. How far from the lens (in cm) must the object be placed to accomplish this task, if the final image is located 12 cm from the lens?

Answer 1

We have magnification. Use it to find the object distance:

$$M=-\frac{i}{o},\\\space\\ o=-\frac{i}{M}=-\frac{-12}{2.2}=5.45\text{ cm}.$$

Since the image is virtual, we used "-" before the image distance.