Alight bulb is placed 20 cm in front of a concave mirror with a focal length of 8 cm.

I guess the problem is asking for the position of the image.

We can solve the problem by using the mirror equation:

where
f is the focal length of the mirror
is the distance of the object from the mirror
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  in the equation, we can find the position of the image:


from which we find

and the positive sign means the image is real.