Problem 3: Suppose that you want to encrypt a message using an affine cipher. You let a = 0,b= 1, etc., but you also include ? = 26, ;= 27, = 28 and ! = 29. Therefore you have 30 symbols to encrypt and your affine cipher is given by ar +b (mod 30). (a) Enumerate all choices for a Z30 that allow you to decrypt. (b) Suppose you try to use a = 12 and b = 3. Find two plaintext letters that encrypt to the same ciphertext letter