Stopping distance-
MpH × The time gap you leave between cars
Ex. If you are going at 20 mph, you must leave a 2 second gap between you and the car in front of you and so the stopping distance is 40 feet. The gap you then must leave between cars goes up by .5s every 10 miles so at 30 you must times it by 2.5 seconds.
Braking Distance-
The stopping distance - MpH
Ex. If you are going at 30 Mph and the stopping distance is 75 feet, then the braking distance is 45 feet as 75-30=45
Thinking Distance-
Easy. The Stopping Distance - The Braking Distance.
The calculations are quite approximate but overall are only out by a couple of inches.