Final answer:
The image height is 0.22 times the object height.
Step-by-step explanation:
The image height can be determined using the magnification formula, which is given by:
magnification = image height / object height
Given that the object height is 18 mm and the image is formed 4 mm in front of the mirror, we can substitute these values into the formula:
magnification = image height / 18 mm = 4 mm / 18 mm = 0.22
Therefore, the image height is 0.22 times the object height. In this case, the image height would be approximately 3.96 mm.