First, we convert it into a unit like this
20 workers × 30 days = 600 units work
After leaving the 5 workers, we have 35 days to complete the work.
In 35 days only 15 workers will do the work.
So the work completed in 35 days by 15 workers = 35 ×15 =525 units
Remaining unit = 600 -525 =75 units
This unit would do by 5 workers in (75/5) = 15 days.
So after 15 days, 5 workers should leave the job.
