Well-explained please!!!

Compute H(K|C) and H(K|P, C) for the Affine Cipher, assuming that keys are used equiprobably and the plaintexts are equiprobable. Recall that by def'n of Affine Cipher, .P = C = Z26 where k = (a, b) E X, ek (x)-ax + b mod26, dk(y)-a1(y - b)mod26 Vx, y E Z26. As we have the values of a E Z2-a- 1,3,5,7,9,11,15,17,19,21,23,25 as gc d(a, 26) 1. That is, we have 12 keys that encrypt x to y for each pair of plaintext/ciphertext