Interest is paid on the amount of the original deposit plus any interest the account has earned

i lokey dunno!

on the low like i frrl frrl dunno jitt

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.