Difficulty levels change the enemy soldiers' abilities.
In each case you have to gain 30000 points.
Solid kill - 1000 points
Easy kill - 500 points
BTR - 4000 points
Truck - 10000 points
You get a bonus for killing enemies quickly.
You begin in front of a restaurant and can choose weapons #1. If you plan on destroying the BTR, take the rocket launcher with you. Weapons with a thermal vision sight are also useful, as some enemies will hide behind smoke #2.
The mission won't begin until you enter the restaurant. A good way is to hide and wait for the enemies to enter the room you're in #1. You can use Burger Town, from which you'll easily destroy both BTRs #2.