lenses

[no idea]

An object pin is placed 20cm in front of a convex lens which is 10 cm away from a plane mirror . An inverted image is found at the same position of the object(above the object).
What is the focal length?
thanks

[Doc Al]

Here are a few hints. Is the image formed by the lens real or virtual? What does a plane mirror do?

Figure out where the image would be if the mirror wasn't there.