Answer:
D
Step-by-step explanation:
If we divide 5 by 6 we'll come up with 8.333 repeating. It is necessary that we round to three decimal places since we have an endless amount of digits that can only be represented with 3 digits
I'm sorry but the solution you proposed was a bit hard to follow, so I'll just post my solution: we convert "2 and 1/2" to a single fraction:

So, we know that 5/2 gallons cost 60 dollars, which means

To find the cost of a single gallon, we have to solve the equation for g:

20 because you are doing 50-30=20 adding x so it would be 20x