Answer: Object of a preposition: support, direct object: letter, indirect object: John.
Explanation: a word governing, and usually preceding, a noun or pronoun and expressing a relation to another word or element in the clause, in the given sentence, the preposition is "of" and its object is "support." A direct object a noun phrase denoting a person or thing that is the recipient of the action of a transitive verb, in the given sentence it is "letter." An indirect object is a noun phrase referring to someone or something that is affected by the action of a transitive verb, in the given sentence is "John."
A prepositional phrase describes the noun in this sentence the prepositional phrase is "of support" it is describing "letter" so the object of the preposition is "letter"
