Explanation

(a) The focal length of the convex lens
$f = \frac{1}{P}m \Rightarrow f = \frac{1}{5} \times 100\ cm$
$\Rightarrow f = 20\ cm,\ u = - 10\ cm$
$\Rightarrow \frac{1}{f} = \frac{1}{v} - \frac{1}{u} \Rightarrow \frac{1}{20} = \frac{1}{v} - \frac{1}{- 20}$
$\therefore v = - 20\ cm$
Therefore, the image will be formed at a distance of $20cm$ on the behind the object