1. Start the China Mission.
2. Go up to your Objective.
3. Watch Cutscene.
4. Do Coop Snipe.
5. Look at top screen and wait until 2nd car is in middle then shoot.
6. Get out to the hover craft in other words back down.
7. Once down kills and money will appear at top left and 30,000 will be added.
8. Press Start, Quit then go to single player campaign mission, select China and redo.
9. Get 30,000 each time.