There is 3 variable, in this case, painters, walls and time(minutes). You need to find how many painters needed and provided information on the walls and time(minutes).
Increasing walls will cause more painter needed. It was reversed in time which was increased time will cause less painter needed.
In this case, you need to divide the variable walls with time since it reversed so: 27wall/9 minutes It equal to : 3 walls/minute
Information provided is: 3 painters= 3 walls/3 minutes Equal to : 3 paintes= 1 wall/minute
To make it 3 walls/minute, the painter needed will be: (3 walls/minute) / (1 wall/minute) x 3 painters= 9 painters
