1050 minutes or 17.5 hours because she worked 10.5 out of the 28 hours, stocking shelves and the rest working in customer service therefore she worked 28 - 10.5 hours in costumer service which is 17.5 hours. As you said there are 60 minutes in an hour so you multiply 17 by 60 = 1020 + 1/2 of 60 = 30 minutes. If you add 1020 and 30 you would get 1050 hours.