The implicit condition of the first sentence of this question is that six workers can process these parts on time.

It's not too difficult to do it with equations. You can think for yourself.

Arithmetic solution:

If two workers are added after two hours of work, the task can be completed two hours in advance. It shows that the workload of six people in two hours was completed by two newcomers, so it is easy to see that two newcomers worked for six hours.

So the original planned time is 6+2+2= 10 hour.

If each person processes 10 more parts per hour than before, the task can be completed 1 hour in advance. Explain that the original workload of 1 hour was completed by 6 people each hour 10,10/= 9 hours.

So the workload of 1 hour is 10*6*9=540 (pieces).

Total number of parts: 540* 10=5400 (pieces)