Answer:  
The graph goes with the third chart   
Step-by-step explanation:
Y starts at 3 and then goes up to 4,5, and then 6 while x starts at 0 and goes up to 1,2, and 3
 
        
             
        
        
        
So 30/48=15/(x+9)
this could be easily solved by recognizing the proportion (the other way is usiing full  algebra and doing multiply both sides by 48(x+9) and then divide both sides by 30 then subtract 9)
30 is 2 times of 15
therefor 48 is 2 times of (x+9)
48=2 times (x+9)
divide both sides by 2
24=x+9
subtract 9
15=x
x=15
        
             
        
        
        
To find the greatest possible product, you need the greatest possible numbers. The largest possible 2-digit number is 99. The largest possible 1-digit number is 9. Therefore, 99 * 9 will be the largest possible product under these circumstances.
99 * 9 = 891
Hope this helps! :)