helllo. need help with introduction to cryptography class

thank you

3. The DES cipher uses a 64-bit key that only has 56 bits of entropy since every 8th bit of the key is generated by XORing the 7 bits that come before it. (a) If an operation consists of randomly choosing a possible DES key and testing if it is correct, how many operations are required to guarantee that the cipher will be broken? (b) If each operation took 2-28 seconds (about 3.7 nanoseconds) approximately how many days would it take to perform this attack? (c) If this attack were performed in parallel on 128 processors, approximately how many days would it take for one of the attacks to succeed