Let volleyball be v and let basketball be b.
v : b = 4 : 7,      b = 21
v : 21 = 4 : 7
v/21 = 4/7
7*v = 4*21
v = 4*21/7
v = 4*3
v = 12
Volleyballs are 12
Hope this helps. 
        
             
        
        
        
Answer:
A. Perfect square Trinomial 
Step-by-step explanation:
Just did its 
 
        
                    
             
        
        
        
The great enclosure was built to have a surplus population and its religious and administrative activities. There fore the answer would be B since they are trying to protect the population and there religion
        
             
        
        
        
Seismic waves
Step-by-step explanation:
An earthquake releases energy as shock waves, the so-called seismic waves, which ripple across the earth's surface. The seismic waves created as they move from the epicentre an earthquake vary.
(from Google)