Explanation :
Static friction is the frictional force between two objects that are at rest. While sliding friction is the frictional force between two objects in contact and are sliding w.r.t each other.
Static friction is usually greater than sliding friction because in static friction the contact forces is more and the interlocking between objects is tight as compared to sliding friction.     
 
        
             
        
        
        
Answer:
D. A zinc Zn contains 30 protons inside the nucleus and 30 electron outside the nucleus
 
        
                    
             
        
        
        
The answer is a tell me if I am wrong.
        
                    
             
        
        
        
So....
imagine the x and y axis or draw it on a piece of paper, a white board or even on your wall if you like. I'm kidding just draw it on a piece of paper
50m up and 20m down 
the dog's displacement is 50 - 20 which is 30
your answer is 30m north