Help!

A digital camera whose lens has a focal length of 20.0mm is used to take a picture of a 10.0cm-tall object that is 20.0cm away. If your answer contains units, write the symbol for the unit after the numerical answer and do not include spaces. a) How far is the image from the lens in centimeters? b) What is the magnification of this object (with sign)? c) How large (in centimeters) will the object appear on the detector once the camera is focused on the object? d) What is the refractive power of the lens used in this camera