Answer:
(a)
Since each bottle holds 17 fluid ounces, then if b is the number of bottles of water and w is the total volume of water in fluid ounces we can set the following equation:

(b)
Now, if b=51,

Therefore, in 51 bottles there are 867 fluid ounces.
(c)
If w=51, solving for b we get:

Therefore, it would take 3 bottles to hold 51 fluid ounces.