It would take them 8.5 hours.
Explanation:
Since they are painting the room together, they would basically each paint half of the room. So if they were painting half of the room each, it would take them half of the time that it would
normally take each of them. Half of Sally's time is 3.5 hours. And half of John's time is 5 hours. When you add them together, you get 8.5 hours.
Hope this helps!
