n3 is about timing.
click on the lamp, the guy standing their will now walk away and crash into some barrels, and then he will move upwards to the 2 barrels stacked on each other. when he is there, quickly click the upper barrel so that it will crush him.
then the jeep comes, wait until the gate opens. as the jeep is about to drive through quickly click the cable below the gate station. this will shut down the lamp, the jeep will spin out of control, crash into the barrel on the road and explode.
the guy below the guard tower will now go to investigate. some other guy will come out between the barracks with a gun. as the two guys meet, click on the one with the gun. he will drop it. the guys now stare at each other.
click on the yellow chest. it will drop, and the guys standing there will throw a grenade, felling the tower. the falling lamp will kill the two guys standing there