Road Kill
First, get a car and follow the blip on your map to reach the target. Speed up and either slam into him to knock him off his scooter, or attempt to spin him out. Spin-outs are accomplished by coming up on either side, and steering into him. Get out and shoot him, and the mission will be complete.
Waste the Wife
First, get a fast, but strong vehicle, like a Sentinal XS. Get to the starting point. Attempt to crash only into your intended target. Repeated hits of things other than the target will result in a premature destruction of your vehicle. When crashing the vehicle, attempt to spin her out. This is accomplished by coming up on the corner fender, and steering into the car.
Autocide
Go and kill all the persons from the zellow cubs. You'll have plenty of time to complete this mission.