Answer:
forgive me if im wrong but i believe it is c
Step-by-step explanation:
 
        
             
        
        
        
4w-7k=28
-7k+4w+-4w=28+-4w
-7k=-4w+28
-7k/-7=-4w+28/-7
k=4/7w-4
:)
        
             
        
        
        
        
To answer this question you should begin with the coin that has a higher value.  If you start with the dime and then just add the correct number of pennies to total $0.40, you will see that you will need 3 dimes ($0.30) and 10 pennies ($0.10).  
I used a guess and check strategy starting with 2 dimes.
        
                    
             
        
        
        
6 percent intrest per year for 5 years I think is the same as 30 percent for 5 years
so $15,000 x .3 is $4500
$15,000 + $4500 = $19,500
not 100 percent sure if this is correct but I think its right. Sorry if im wrong.