Mission One Answers: New York City and Washington DC were destroyed by nuclear bombs. In Gray Extraction we find out that Richmond Virginia has become New Washington.
Mission Two Answers: Check Walsh's phone number. 1984-3451. The books are 1984 and Fahrenheit 451 where the 3 is a F.
Mission Four Answers: Hint: Figure out the code from the two prisoners in the basement of Central Perception Headquarters.