One person can make n objects in an hour. Ann begins at 10:00 \mathrm{~AM}, Bob begins at 10:20 \mathrm{~AM}, then Cody and Deb begin at 10:40 \mathrm{~AM}. Working at the same constant speed, by 11:00 \mathrm{~AM}, they have made 28 objects. What is n?