You'll start off with the SMG and the Battle rifle. Switch to your SMG, then wait for Sergeant Johnson to get off the crashed Pelican. Swap your SMG for his Sniper Rifle. Now, switch back to your Battle Rifle and enter the doorway. There should be a Minor Grunt. Shoot him in the head with your Battle Rifle or melee him, and continue through the next doorway. Once you're done, either go left or right to confront some Grunts & Elites in Hotel Zanzibar. Kill the Elite as he poses more of a threat with his turret, then kill the Grunts, who would all be Minor or Major.