An affine cipher is a version of a monoalphabetic substitution cipher, in which the letters of an alphabet of size m are first map to the integers in the range 0 to m-1. Subsequently, the integer representing each plaintext letter is transformed to an integer representing the corresponding cipher text letter. The encryption function for a single letter is E(x) = (ax + b) mod m, where m is the size of the alphabet and a and b are the key of the cipher, and are co-prime. Trudy finds out that Bob generated a ciphertext using an affine cipher. She gets a copy of the ciphertext, and finds out that the most frequent letter of the ciphertext is "R", and the second most frequent letter of the ciphertext is "K". Show how Trudy can break the code and retrieve the plaintext.