Jeff likes racing his little sports car, but he knows that safety should always be kept in mind, so he practices regularly. On one particular day, Jeff goes out to the practice track and does two laps at an average of 100 km/h, two laps at an average of 102 km/h, two laps at an average of 140km/h and two laps at an average of 150 km/h. Now Jeff would like to know what his average speed was during that practice session. Can you help him?