1 man takes 22 days to do the job; 1 woman would take twice as long = 44days; 1 boy would take three times as long = 66 days.
So the rates of working are:
man=1/22 of the job per day; woman=1/44 of the job per day; one boy=1/66 of the job per day..
In one day, therefore, if they work together they will complete:
1/22+1/44+1/66=(6+3+2)/132=11/132=1/12 of the job.
So it will take them 12 days to do the job.