If a slide is placed 32 cm from the lens and its focal length is 30. cm, how far away should the screen be placed to obtain a clear image?

4.8 m

Explanation:

The screen should be placed at at the distance at which the image formed by the lens appears, and this distance can be found by using the lens equation:

where

f=30 cm is the focal length (I assume it is a convex lens, so the focal length has positive sign)

p=32 cm is the distance of the object from the lens

q is the distance of the image from the lens

Re-arranging the equation and replacing the numbers, we can find the value of q:

so, the screen should be put at 4.8 m from the lens.