The image of a small electric bulb fixed on the wall of a room is to be obtained on the opposite wall 3 m away by means of a large convex lens . What is the maximum possible focal length of the lens required for the prupose?

Question

$\begin{array}{1 1} 75\;cm \\ 7.5\;cm \\ 0.75\;cm \\ 75\;m \end{array} $