Question

A convex lens produces an upright irnage magnified three times of a given object which is kept 1.5 m away. Its focal length is

Answer 1

Convex lens always form real and inverted images.

The image can be small, big or same size depending on the position of the object from the lens.

The image is always forms on the other side of the lens.

In your question answer is also there

If you place the object 20cms always you will get same size image on the other side of the lens at 20 cms (2)R.