Answer:
I highly recommend that it must be the second story
 
        
             
        
        
        
Answer: 
The answer is -1 / 6
Step-by-step explanation:
use the formula y2 - y1 / x2 - x1 = m
7 - 8 / 10 - 4 = -1 / 6
 
        
                    
             
        
        
        
So first create and define your variables:
Z = amount of zebra fish
N = amount of neon tetras
Now create your equations:
2z+2.15n=31.20
z+n=15
This is your system. There are multiple methods to use but in this problem I’ll use the substitution method by simplifying the bottom equation.
2z+2.15n=31.20
z=15-n
Now I’ll plug the bottom equation into the top one.
2(15-n)+2.15n=31.20
And just solve from here.
30-2n+2.15n=31.20
0.15n=1.20
n=8
So he bout 8 neon tetras, and 15-8= 7, so he bought 7 zebra fish
        
                    
             
        
        
        
Answer:
Adding like terms! Hope this Helps!