Having trouble with these prepositional phrases here:

Please notify me of the type of prepositional phrase used below:

I really love banana cupcakes with frosting.

I believe the phrase is with frosting.
does it function as a:
adjective
adverb
locative
instrumental
or
possessor

Also:
Roxanne is the worst cook on the team.

What is cook?
a
subject
direct object
indirect object
or
predicate noun
Thanks guys!!!!