10 pieces there was five people each got two pieces
        
                    
             
        
        
        
Midpoint formula: (x1+x2/2 , y1+y2/2)
So,  (-1+3/2  , 9+8/2)
-2/2 = -1      17/2 = 8.5
Answer: (-1,8.5)
        
                    
             
        
        
        
Okay first you would ask yourself 
What plus ten will give you fifteen?
And it would be five
Then multiply five by the three
And you’d get 15
So it would be
X=15
( 15/3 + 10 =15)
        
             
        
        
        
-5, because subtracting a negative is the same as adding a positive, which will bring -9 up to -5