Answer:
They get 4 good points!
Step-by-step explanation:
21-17= 4:)
 
        
             
        
        
        
Answer:
1/10th
Step-by-step explanation:
 
        
             
        
        
        
Since the scale factor is smaller than one (the original), the resulting image is smaller than the original. 
Hope this helped, and feel free to ask more questions if needed(: 
 
        
                    
             
        
        
        
3:27
And another one would be 
9:81
        
             
        
        
        
If you mean  proof that the opposite sides of a parallelogram are equal, you draw a diagonal then prove that the 2 triangles formed are congruent.