Parallel = same slope
y = -2/3x + b
Plug in point
15 = -2/3(-3) + b
15 = 2 + b, b = 13
Solution: y = -2/3x + 13
The decimal representation of any number is a linear combination of powers of 10. In other words, given a number like 123.456, we can expand it as

for any
, so the above is the same as

Similarly, we can write

Now it's a question of reducing the fraction as much as possible. We have
so

72 cups (US Gallons)
1 gallon = 19.215 cups.
The answer to this question is x=6