Can someone explain to me how to do this problem ?

The image distance is 13.3 cm  ⇒ answer B

Explanation:

* Lets study the information in the problem

- The distance between the object and the convex lens is 40.0 cm

- The lens focuses light at a distance of 10.0 cm

- The equation of the image distance is

 where di is the image distance, do is the object distance and f is the

 distance of the focuses lens

* Lets solve the problem

∵ do = 40.0 cm

∵ f = 10.0 cm

∵

- Substitute the values of do and f in the equation

∴

∴ di = 13.3333 ≅ 13.3 cm

* The image distance is 13.3 cm

real, smaller and upside-down.   so the answer should be b.

measure their densities same density, same sub