please provide answer with steps.

3.7. A DES key Kw is called a weak key if encryption and decryption are identical operations: DESKw (x) DES-1 Kw (x), for all x 1. Describe the relationship of the subkeys in the encryption and decryption algorithm that is required so that Eq. (3.1) is fulfilled. 2. There are four weak DES keys. What are they? 3. What is the likelihood that a randomly selected key is weak