Rosa can paint a room in 12 hours. hanna can paint the same room in 9 hours. how long does it take for both rosa and hanna to paint the room if they are working together?

Rosa can paint 1/12 of the room in a hour

Hanna can paint 1/9 of the room in a hour

Together they can paint 1/9+1/12 of the room in a hour or 7/36 of the room

Since they can paint 7/36 of the room in a hour. They paint the whole thing in 36/7 hours.