Answer:
it would be C. 
Step-by-step explanation:
if you have 7 dogs and take away 7 you have 0 dogs.
 
        
                    
             
        
        
        
First:
2x + 2z = 4
2(x+z)=4
x+z=4/2
x=2-z
-x - y - z=  -8
-(2-z)-y-z= -8         replace x
-2+z-y-z= -8          (cancel z)
-2-y= -8
6 = y
Then:
-4x + 4y + 5z = 7  replace x and y
-4(2-z)+4*6 + 5z = 7
-8 + 4z + 24 + 5z = 7
16 + 9z = 7
9z = 7 - 16
9z = -9
z = -9/9
z= -1 
Finally
x= 2-z  replace z
x = 2- (-1)
x = 3
 
        
             
        
        
        
I hope this helps you
2 (B+4)=3
B+4=3/2
B=3/2-4
B=-5/2