(-2.5,6.1)(-2.5,3.1).....notice how ur x values are the same. This means that u have a vertical line which has an undefined slope.
IF ur y values would have been the same, u would have had a horizontal line which has a 0 slope.
        
             
        
        
        
What we know: 
-volume of 10,000 drops is 10 fluid ounces
Step 1: Divide 10,000 by 10 (to find how much we need to divide 10 by to get our answer)
10,000/10=1,000
Step 2: Divide 10 by 1,000 (to find our answer)
10/1,000=0.01
Our answer is 0.01. The volume of 10 drops of liquid is 0.01 fluid ounces.
        
             
        
        
        
There are 500 ones in 500