Final answer:
The magnification of the optical device is -3.
Step-by-step explanation:
The magnification of an optical device can be determined using the magnification formula: m = di/do, where di represents the image distance and do represents the object distance. In this case, the object is 20 cm wide and appears inverted with a width of 60 cm. To find the magnification, we can use the formula m = -di/do, where the negative sign indicates that the image is inverted.
Let's substitute the given values into the formula:
m = -60 cm / 20 cm = -3
Therefore, the magnification of the optical device is -3.