Solve all parts a,b & c step by step

Consider a substitution/transposition cipher which encrypts blocks of mn bits by dividing the block into n words of m bits in size. Encryption proceeds with each m-bit word of the block being substituted by another m-bit word based on the key (with the same substitution key used for each word), followed by the transposition of the words within each block based on the key (with each transposition key the same for all blocks). Consider a version of the cipher with m=4 and n=8. (a) Determine the size of the key space. (b) Assuming a redundancy of RL=75%, determine the unicity distance (in bits) of the cipher. (c) Determine a lower bound on the expected number of spurious keys if 32 bits of ciphertext are available. Repeat for 64 bits and 96 bits of ciphertext