Ms. Hershey rewards students with a piece of chocolate (approximately 60 calories) for every day that they hand in an assignment. David handed in 7/8 of Ms. Hershey’s assignments over the past school year. Given that 30 minutes of play burns 150 calories, how many assignments did Ms. Hershey assign if it took David 28 hours to burn off all the calories from the chocolates he earned?