The following string represents a ciphertext of an english sentence encrypted using the Vigenere cipher :

QMVHGYBMRLLMUCUXRRQGTGBBFYBKNN

You manage to learn that the key is 4 characters long. Your reconnaissanceefforts also observe the following partially decrypted ciphertext:

donotYBMRLLMUCmeeRQGTBBFYrap

a) Use the cipher text and partially decrypted ciphertext to recover the encryption key.

b)Using the key you recovered in part -a , recover the full english plaintext.