There are a total of 6 people working, and each person takes 2 minutes to prepare one bag. That is an average of 3 bags per minute. Then you take 900/3 which is 300 minutes to finish all of the bags. The question asks how many HOURS it takes so you need to convert 300 minutes into hours by dividing it by 60 since there are 60 minutes per hour. 300/60=5 so it takes her and her friends a total of 5 hours.