The mirror formula for curved mirrors is:

where
f is the focal length of the mirror

is the distance of the object from the mirror

is the distance of the image from the mirror
The sign convention that should be used in order to find the correct values is the following:
-

: positive if the mirror is concave, negative if the mirror is convex
-

: positive if the image is real (located on the same side of the object), negative if it is virtual (located on the opposite side of the mirror)
You are correct because nothing is being done to the cake
They all move through empty space at the speed of light
Perilymph of scala vestibule; endolymph of cochlear duct; perilymph of scala tympani
Speed is distance over time, learn that formula and look at the image