Read the sentence.

we're trying to find out whose car is parked in front of our driveway.

how is the form of who or whom used?

object of a preposition

subject

direct object

possessive

The correct answer is: possessive

Explanation:

Whose is the possessive form of the pronoun "who", which means that it is used to mention the thing a person owns (possession). If we break down the sentence, the function of this word will be more clear:

A car is parked in front of a driveway.

This car belongs to someone.

We are trying to find out who has this car as their possession.

"whose" links all this information into a single sentence: We're trying to find out whose car is parked in front of our driveway.

as for symbolic actions, the narrator's tearing down the wallpaper in an attempt to find the "woman" in the wallpaper represents her struggle to retain or regain her sanity.   the wallpaper has been part of her confinement and by her tearing it down, she is freeing herself from that confinement.