There are 6 total instances of Tank Mayhem.
- 3 in Loren Square (Easy is north of the fill-her-up shop, Medium is right near the border with Sunset Park, and Hard east of the Havemayer Estates)
- 2 in Camano Place (Easy is south of Curly's Chop Shop Block, Medium is East of the gun shop)
- 1 in Rosen Oaks (right next to the image as designed)
The goal is to rack up enough damage in $ to reach the goal. It's one of the most fun in my opinion and also one of the easiest activities. If you're struggling, just keep shooting the cannon with LT at anything whether it be cars, tanks, people, even lightpoles. Just don't let the combo bar go down, and it should be a breeze. Have fun!