types of authentication, writing homework help

Explain the threat in each of the following types of authentication and provide a solution for each scenario below:

Alice sends a password, and Bob compares it against a database of passwords.
Alice sends a password, and Bob hashes it and compares it against a database of hashed passwords.
Alice computes the hash of a password and uses it as secret key in challenge/response protocol.
Alice computes the hash of a password and sends it to Bob, who hashes it and compares it against a database of doubly-hashed password