X^2-10x-24=0
(x+2)(x-12)=0
x=-2 or x=12
        
                    
             
        
        
        
2x-4y=-16
ax+4y=6      +
--------------------
2x+ax=-10;     for x=-2, 
2(-2)+a(-2)=-10
-2a=-10+4
a=-6/-2
a=3
        
             
        
        
        
Answer:
-4
Step-by-step explanation:
The common difference is found by subtracting the second term from a previous term
So...
3-7 would give the common difference = -4
-1-3 would give the common difference= -4
-5-1 would give the common difference= -4