12x50=600 so 60 left
15x50=750 so 60 left
so the administration fee is 60
        
                    
             
        
        
        
(5x+1)² = 7; expand: 25x² + 10x +1 = 7 or 25x² + 10x -6 = 0
Solve this quadratic for x:
x = [-b + √(b² - 4ac)]/2a and x = [-b - √(b² - 4ac)]/2a 
Plug the values and you'll find :
x = (- √7 - 1)/5 (answer C)
x = (+√7 -1)/5  (answer E)
        
                    
             
        
        
        
The best group to take a sample from would be the eighth graders because they are the ones who will be participating in the dance, so they should have the most input.