I guess the problem is asking for the position of the image.
We can solve the problem by using the mirror equation:
[tex] \frac{1}{f}= \frac{1}{d_o}+ \frac{1}{d_i} [/tex]
where
f is the focal length of the mirror
[tex]d_o[/tex] is the distance of the object from the mirror
[tex]d_i[/tex] is the distance of the image from the mirror
For the sign convention, the focal length is taken as positive in a concave mirror. If we use f=8 cm and [tex]d_o =20 cm[/tex] in the equation, we can find the position of the image:
[tex] \frac{1}{d_i} = \frac{1}{f}- \frac{1}{d_o}= \frac{1}{8 cm}- \frac{1}{20 cm}= \frac{3}{40 cm} [/tex]
from which we find
[tex]d_i = \frac{40 cm}{3}=+13.3 cm [/tex]
and the positive sign means the image is real.
