When you spawn, have all players go right, shoot the bell and throw a grenade at the door. Finish off all enemies that are around and go up the stairs to the left of the door. Breach charge the door and open and close the door while standing against it. About after 15 seconds blow it. Kill everyone else around and go to the second building over the catwalk and open the doors and breach the inner doors of the office with 4 computer screens on a curved table. Blow that door and then run inside and throw a grenade, run back out and go to the door opposite to the one you came into the building by. Breach that door, have another player walk down the stairs and look around the corner three times and run back up and you should be able to see through the door and count the enemies. Blow it and you should be done