Easy peasy, this is a representation of differnce of 2 perfect squares
a^2-b^2=(a-b)(a+b)
        
                    
             
        
        
        
I believe it would be any number that is within the darkest shaded area. (-4,1) seems like it would be correct.
        
                    
             
        
        
        
 
x=4 y=5
if we put two pharases together 
the answer is as follows pic :
x=4 y=5
 
        
             
        
        
        
Answer:
5
Step-by-step explanation:
40÷[20-4*(7-4)]
Start with the inner most parentheses
40÷[20-4*(3)]
Then the brackets, multiply first
40÷[20-12]
Then subtract
40÷[8]
We are now left with the division
5