Answer: The magnification of the image is 0.50. This means the image is half the size of the object.
Step-by-step explanation:
The magnification (m) of an image produced by a mirror is given by the ratio of the image distance (di) to the object distance (do). The formula is:

In this case, the object distance (do) is 18 cm and the image distance (di) is -9 cm (the negative sign indicates that the image is virtual and located behind the mirror). Substituting these values into the formula, we can calculate the magnification.
The magnification of the image is 0.50. This means the image is half the size of the object.