Question 721554
First find the rate at which one person does the job.  Once found, multiply by 3.  Use rate in the form of jobs/time.


Letting r = rate of a single worker,
4r = the rate for the four people working together, 1 job in 3 days, or 1/3 jobs/day.


{{{4r=1/3}}}
{{{r=1/12}}}, jobs per day, FOR ONE PERSON DOING THE WORK ALONE.
...
Finish it!