If the work efficiency is improved by 20% from the beginning, that is, the original 1+20%=6/5, then the time is 5/6, and the task can be completed three days in advance, and the original planned time is 3/( 1-5/6)= 18 days.

The work efficiency is improved by 25%, that is, the original: 1+25%=5/4, and the time is 4/5. Results The task was completed two days ahead of schedule, and the original time was 2/( 1-4/5)= 10 days.

Therefore, the original production time of 16000 was: 18- 10=8 days, and the original plan was to produce 16000/8=2000 pieces per day.

Then, the task of this batch of production is: 18*2000=36000.