Answer:
There is a cost-saving of $1,000 per month as a result of the change.  This cost-saving increases the monthly net operating income by $1,000.
Explanation:
a) Data and Calculations:
Fixed monthly expenses = $17,000
Current sales units per month = 800
Proposed sales commission per unit = $5
Decrease in salaries per month = $6,000
Increase in sales units per month = 200
                                                  Change
                                             Before       After      Difference
Fixed monthly expenses   $17,000   $11,000      $6,000
Variable cost per month               0     5,000       -5,000
Total cost per month         $17,000  $16,000      $1,000
Sales units per month              800      1,000           200 units
b) The effect on the company's monthly net operating income is a reduction in the total cost per month by $1,000.  There is also an increase in the units sold per month by 200 units.  If the selling price is determined, the net operating income will also increase by the product of the contribution margin per unit and 200.