Let's use the mirror equation to solve the problem:
where f is the focal length of the mirror,
the distance of the object from the mirror, and 
the distance of the image from the mirror.
For a concave mirror, for the sign convention f is considered to be positive. So we can solve the equation for by using the numbers given in the text of the problem:
Where the negative sign means that the image is virtual, so it is located behind the mirror, at 8.6 cm from the center of the mirror.
where f is the focal length of the mirror,
For a concave mirror, for the sign convention f is considered to be positive. So we can solve the equation for
Where the negative sign means that the image is virtual, so it is located behind the mirror, at 8.6 cm from the center of the mirror.
