Master Feng, Daye fortune teller.

Because the total number of parts (total workload) remains the same, the working efficiency is inversely proportional to the working time.

Less than 20 pieces are processed per hour, which takes 4/3 of the planned time, which means the work efficiency is 3/4 of the planned time.

Therefore, it is planned to handle it every hour: 20÷( 1-3/4)=80 pieces.

If 10 pieces are processed every hour for the second time, the working efficiency will be (80+ 10)÷80=9/8 as planned.

So the time is 8/9 of the plan.

So the planned time: 1÷( 1-8/9)=9 (hours)

So the total number of parts is 80×9=720 (pieces).