it is called ones period system .this is based on international system of numeration.
 
        
             
        
        
        
It is 252. hope I helped!
        
                    
             
        
        
        
Answer:
100
Step-by-step explanation:
hope this helped :D
 
        
                    
             
        
        
        
12^2 +b^2 = 20^2 because of the Pythagorean theorem 
144 + b^2 =400
B^2 =256
B=16