Answer: 
 the gross monthly income last month is $3,318.92 
Step-by-step explanation: 
 The computation of the gross monthly income last month is shown below: 
 = Total sales × commission percentage 
= $82,968 × 4% 
= $3,318.92 
hence, the gross monthly income last month is $3,318.92 
We simply multiplied the total sales with the commission percentage
Explanation: