Three workers can do a job in 28 hours. How many more workers are needed to do this job in 12 hours?

4 additional workers for 7 total workers.

if it takes 3 workers 28 hours to do work there are 84 total hours of work (3*28=84) to find how many workers it will take to get the work done in 12 hours divide 84 by 12. 84/12 = 7 total workers. 7-3 = 4 additional workers needed.