In rampage 3 Trevor has 2 minutes to kill 30 gang members using grenades and an assault rifle.
Kill the gang members in the car first and then go up the alley way which will force more gang members to spawn. This allows you to massacre more of them in the time limit given. There are gang members who will spawn on top of the roofs, so be sure to be weary of them. Always use the mini map to your advantage, and aim for the head.