18         
            
 
            
 
            
 
            
 
            
 
            
 
            
 
            
 
            
 
            
 
            
 
            
 16, 17, 18, 19,20         
            
 
            
 
            
 
            
 
            
 
            
 
            
 
            
 
            
21         
            
 
            
 
            
 
            
 16,17         
            
 
            
 
            
 
            
21         
            
 17, 17.5, 18, 19, 20,21, 21.5