The answer is not any of the letters. I got x=15/2 or x=7.5. You may have made an error in your question.
You would take the 36 and divide it by the 3 then add 6
The amount of water decreases
pints in 12 weeks.
Solution:
The amount of water decreases in 7 weeks =
pints
The amount of water decreases each week is same.
Let us first change the mixed fraction into improper fraction.
pints =
pints
The amount of water decreases in 1 week



So, the amount of water decreases in 1 week is
pints.
The amount of water decreases in 12 week



pints
Hence the amount of water decreases
pints in 12 weeks.
Multiply 1/6 by 3 =1/2
In 3 days she would have completed 1/2 of the scarf.