The ciphertext FTQIMKIQIQDQ was encrypted using the encryption function E: Z26 Z26 where E() = (

Question:

The ciphertext FTQIMKIQIQDQ was encrypted using the encryption function E: Z26 → Z26 where E(θ) = (θ + k) mod 26. Considering the frequencies of occurrence for the letters in the ciphertext, determine (a) the key k for this cipher shift; (b) the decryption function D; and (c) the original (plaintext) message.