Cryptanalysis affine cipher and substitution cipher

1) Consider the chosen-plaintext attack on the simple substitution cipher. How many chosen plaintext characters suffice to uniquely determine the key?

2) Consider the chosen-ciphertext attack on the simple substitution cipher. How many chosen ciphertext characters suffice to uniquely determine the key?

My answer was: 2 over 26.

3) Using a brute force approach, roughly how many keys would need to be searched on average before guessing the key of the simple substitution cipher? How would one detect that the correct key has been guessed?

My answer was: more than 177 years at 2 over 56 keys/seconds.

4) Consider the chosen-plaintext attack on the simple affine cipher. How many chosen plaintext characters suffice to uniquely determine the key?