Sudha finds out that the sharp image of the window pane of her science laboratory is formed at a distance of $15\, cm$ from the lens. She now tries to focus the building visible to her outside the window instead of the window pane without disturbing the lens. In which direction will she move the screen to obtain a sharp image of the building? What is the approximate focal length of this lens?

• A
  Towards the lens; $15\, cm$
• B
  Away from the lens; $15\, cm$
• C
  Towards the lens; $30\, cm$
• D
  Away from the lens; $30\, cm$