formula and steps to solve? thanks

4. (3 pts) You are using a magnifying glass to read a small print. If you hold the magnifier at 2.0 cm from the text, what focal length should the magnifier have if the image is 4 times larger than the object? A) 2.7 cm B) 3.6 cm D) 4.0 cm D) 8.2 cm E) 16.0 cm