6. The following ciphertext PULCL YTHRL LEJLW APVUZ HULEJ LWAPV UKPZW YVCLZ AOLYBSL was obtained using a Vigenre cipher with a keyword of length p. Here is the frequency table for the letters in this ciphertext A | B | C | D | E | F | G | H | 1 | J | K | L | M ?N?O 31202002021 10 0 01 40 1 1 1 4 33 0 3 3 (a) Compute the index of coincidence and use it to estimate the length of the keyword. (b) Decrypt the ciphertext