OMG im suffering in this too
but im starting to get this so lets take a look
i tried writing an equation but all i get is one so
answer is one and slope is 0 hope i could help

solve for "K", to see what "K" is, or the "constant of variation",
once you found K, plug it back in y=Kx, and that's the equation
4 can hold 8 gallons = 8/4 = 2 big bottle per gallons.
For 10 big bottles = 10 x 2 = 20 gallons.
If you are looking for how many bottles can be filled with 10 gallons, the answer is 5.