Convex Lens Problem: Find Focal Length

[Siddharth Venu]

A screen is placed 90cm from a object. The image of the object on the screen is formed by a convex lens at
two different locations separated by 30cm. The focal length of the lens is what?

 

[Herman Trivilino]

You can't just post a homework question and expect to get a response here. Start another thread, use the template, and show some effort towards a solution. You get help here, not answers.