The answer is 42kg/45kg or 14kg/15kg
        
             
        
        
        
Do you mean how you can tell between an area formula and a volume formula? Well usually like on a reference sheet it says the shape and the letter a or v, a representing area and v representing volume. I hope this helps, if it doesn't please tell me in the comment section
        
                    
             
        
        
        
Answer:
A: 8+9+10=27
    9+10+11=30
    10+11+12=13
B: 19+20+21
C:  There isn't any.
Step-by-step explanation:
It just is lol.