Final answer:
The subject of the sentence is 'not much damage' and the sentence is in the passive voice.
Step-by-step explanation:
In the sentence “Fortunately not much damage was done by the fire,” the subject is “not much damage.” The sentence is in the passive voice because the subject is being acted upon rather than performing the action. In active voice, the sentence would be “Fortunately, the fire didn't do much damage.” Passive voice is used when the focus is on the receiver of the action rather than the doer. It is often used when the doer is unknown or unimportant.