If you know how to get to the Katana get it (it's listed on this site), second get the machine gun, third go to the Plaza with the grocery store in it.

There should be a guy with a shotgun, kill him and take his weapon.

Then go to Adam. once you encounter him, wait for him to start blowing the balloons.

Use the machine gun to knock him out and keep firing till you run out of ammo.

Then use the Katana when he is still knocked out (the most amount of time he will be knocked out is about 20 seconds so do it fast).

He will then be weakened, wait for him to blow his balloon, shoot it and then shoot him again with the shotgun.

Adam will be dead, but wait there is more - you now have a shotgun with at least 10 bullets left in it's chamber.

Use it wisely if you want to survive!