Focal length

[Spike]

A astronomical telescope is used to project a real image of the moon on the screen 25 cm from the eyepiece, which has a focal length of 5 cm. How far must the eyepiece be moved from its normal position. Can anyone help me how to work this one out

[Fu-Kwun Hwang]

Hint:
It is a telescope, so the moon can be treated as an object located at infinite.
So the image is form at the focus point.

You might be able to work out the rest! :-)