Answer:
-30
Step-by-step explanation:
i am not sure just remember getting taught it. 
 
        
             
        
        
        
It would be C because a coefficient is always with a variable and 6 is with a variable which makes it a coefficient 
Hope this helps
Have a great day/night
        
                    
             
        
        
        
D because the submarine started at sea level and ended 400 meters BELOW sea level.