Thank you for posting your question here at brainly. I hope the answer will help you. Feel free to ask more questions here.
First find a common denominator between 4hours and 3hours. => 12 hours
In 12 hours Mona can paint 3 rooms
In 12 hours Lisa can paint 4 rooms
In total they can paint 7 rooms in 12 hours.
To paint 1 room, they need 1/7 of the time.
12 * (1/7) = 12/7
so 12/7 hours
