These are missions five and seven. These are hard because they are VERY small, filled with enemies, and there are many places where enemies can ambush you.
Takedown: This is a small map with many enemies and many civilians. Take it slow, I mean, VERY SLOW. DO NOT SHOOT unless you know it is a bad guy. After you pass the gate with the dog, take it slower. There is VERY little space to move and many places where you can get ambushed. This was one of the hardest parts of the game, just go into a building, kill the enemies and move on. There are no infinite respawns.
Hornet's Nest: You really have to slow down. To pass the gate, run to cover and kill the enemies, eventually a Technical will come and break the game. The market is small and filled with enemies with shotguns, so take it very slow and kill the enemies. When you miss the jump, run fast as the enemies will be after you and you have about a minute to reach the chopper. Don't worry about killing anyone, just keep sprinting.