I've been stuck on these problems for a couple days - can you help explain them to me (I know they're probably super easy but)?   1

I've been stuck on these problems for a couple days - can you help explain them to me (I know they're probably super easy but)?

1. A random plastic lens is found on the beach.  In an object sitting 25.0 cm in front of the lens forms an 

image 20.0 cm behind the lens,

a.  What is the focal length of the lens?

Answer ______

b. Is the lens converging or diverging?  How did you know?

Answer ______

2. The focal length of a converging lens is 17 cm. A 5 cm tall light bulb is placed 34 cm in front of the lens.    

Determine the distance from the image to the lens. Show your work.

Answer ______

3.  Giorgio is clicking shots of toy sailboats in a pond.  The camera contains a lens with a focal length of  0.0500 m.  

a.  How far back must the film be located when the boat is 3.00 m from the camera?  

Answer ______

b. Should the lens be moved in or out as the boat approaches the photographer?

Answer ______