For Cops, there are 20 tiers of missions, each has 3 assignments you can pick. Cop choices are Patrol, Undercover, and Enforcer.
Cops also have 3 different types of Missions: Rapid Response, Interceptor, and Hot Pursuit.
Rapid Response will have you going from point A to B under a certain time and you are penalized time by hitting cars and walls.
Interceptor you have take out a single racer in under 2 minutes. Easiest done using EMP and Electrostatic Field(ESF).
Hot Pursuit you have to take out all racers before the end of the race. Easy difficulty has 4 racers, medium has 5, hard has 6.
When picking your assignments the ones that require interceptor missions are the easiest and the ones that require Hot Pursuit are going to be the hardest. Also, the missions that require you to earn a specific amount of money, if you just do interceptor missions you can use EasyDrive (
) and restart the mission.
As you go through the story you can only pick one assignment at each tier of the story, putting you at level 21 when you beat the game. At this point, the game will let you go back and do the other 2 assignments for each tier.
You will receive rank 20 achievement once you unlock the final mission.
You will receive rank 40 achievement for finishing 40/61 assignments.
You will receive rank 60 achievement for finishing 60/61 assignments.
Extra: For people who are having issues with the save glitch, the best method I have found to work is when you are done playing the game. Go to your home screen, open the start menu over the game and click the quit option. Once I started doing this every time I was done playing, I never had it lose save progress.