Go outside and kill a few enemies,

previous level, there are many enemies.
Kill all of them and enter the garage, just before you enter you are locked in, wait for the enemies to open the roll-up door on the other side and kill them all to get out. Enter the bus and get out through the back door, please be careful when getting out. Near the door an RPG flies over and Blake is blown away, get up and blood the three enemies outside the BUS, they all have torches on and it's easy to confirm their position. Get out of the car and follow the same route back to the school from the previous level.