Answer: 18 quarts
Step-by-step explanation:
Quantity of sparkling water and gape juice are used in proportion in the recipe.
Let x= quantity of sparkling water when 9 quarts of grape juice is used.
Then,
[tex]\dfrac{x}{9}=\dfrac{1\dfrac12}{\dfrac34}\\\\\Rightarrow\ =\dfrac{x}{9}=\dfrac{\dfrac32}{\dfrac34}\\\\\Rightarrow\ \dfrac{x}{9}=\dfrac{4}{2}\\\\\Rightarrow\ x= 2\times9\\\\\Rightarrow\ x=18[/tex]
Hence, 18 quarts of sparkling water is required to mix with 9 quarts of grape juice.