There is one encryption algorithm called Affine Cipher, with encryption function E(x)- (ax + b) mod 26. Here, x is the numerical equivalent of the given plaintext letter, a and b are appropriately chosen integers. The numerical equivalents of the letters are as follows: 012 3 456 7 8910 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 Encrypt plaintext IT WILL BE DELIVERED TO YOU AT FIVE PM using affine function 7x +9 mod 26. What is the decryption function? Show that it works. a. [10 marks] b. Consider an affine cipher (mod 26). You are doing a chosen plaintext attack using lalala and the cipher text is popopo. Determine the encryption function with explanation of the steps. [15 marks]