since this is a work problem then we'll have rate.
15 workers can finish the job in 30 days so we'll have the rate as
R = 1/(t×n)
(R=rate per person)
R = 1/(30×15)
R = 1/450
----
If there are only 6 workers then
R=1/450
n=6
R=1/(t×n)
(1/450)=(1/6t)
cross multiply
6t=450
t=75
therefore it takes 75days for 6workers to do the same job.
