If an object is placed at the focus of a convex lens, where is the image formed?

A 1 cm high object is placed at a distance of 2f from a convex lens. What is the height of the image formed?

If the image formed by a convex lens is of the same size as that of the object, what is the position of the image with respect to the lens?

Where should an object be placed in order to use a convex lens as a magnifying glass?

Where should an object be placed in front of a convex lens so as to obtain its virtual, erect and magnified image?