Robert paints 1/6 of a room in an hour.
Julio paints 1/8 of a room in an hour.
Working together, they can paint (1/6 + 1/8) room/hour =
(4/24 + 3/24) room/hour =
7/24 of a room per hour.
7/24 of a room per hour means
24 hours / 7 rooms =
(24 / 7) (hour/room) = (3 and 3/7) hour per room.