2 people working at the same rate will take 9 hours to paint a room. Assuming that they all work at this rate, how long will it take 3 people to paint the room?

So if 2 people take 9 hours to paint the room and you want to know how long it will take if 3 people were painting first you will have to find the slope, or the rate of change, to do this you have to divide 9/2.
9/2= 4.5
So it take 4.5 hours for one person to paint the room.
Therefore if there where three people painting it would be 3 x 4.5= 13 hours and 30 minutes.
The time it would take to paint the room would increase.