Answer:15
Step-by-step explanation:
Given
Craftsman sell 10 Jewelry set for $500 each
For each additional set he will decrease the price by $ 25
Suppose he sells n set over 10 set
Earning
Earning 

differentiate to get the maximum value 

Equate  to get maximum value
 to get maximum value 



Thus must sell 5 extra set to maximize its earnings.
 
        
             
        
        
        
Use distributive property in order to find the equivalent pieces of oi
        
             
        
        
        
The answer is 70 the third option.