If dozier had produced 1,001 units instead of 1,000 units, how much incremental manufacturing cost would it have incurred to make the additional unit?

The additional cost will be total variable cost per unit.

For example assume that total variable cost per unit for the unit is $2 and the selling price of unit product is $5. The fixed cost is $100,000 and the unit produced are 35000

Now

Total cost for 35000 units = $100,000 + $2*35000 units = $170,000

Now assume that we have produced 35001 units,

Total cost for 35001 units = $100,000 + $2*35001 units = $170,002

The additional cost is $2 per unit which is Total variable cost per unit.