Answer:
The net operating income will c. increase by $7,000
Explanation:
The formula to calculate net operating income  is =
Gross income - Operating expenses 
If  Sales are equal to 200 units  and the payment for a salesperson is
a flat salary of $5,000 
Gross income  = 200  * $80 = $16,000 
and
Operating expenses = $5,000
so
Net operating income = $16,000  - $5,000 = $11,000
If  we rise the Sales to 300 units then the payment for the salesperson will be 20$ * 300 = $6,000.
Gross income = 300  * $80 = $24,000
and
Operating expenses = $6,000
so
Net operating income = $24,000 - $6,000 = $18,000
 $18,000 -  $11,000 = $7,000