Final answer:
To find out how much garlic powder is used with 18 teaspoons of salt, we use the ratio of garlic powder to salt in the given double batch.
Step-by-step explanation:
To find out how much garlic powder is used with 18 teaspoons of salt, we need to determine the ratio between garlic powder and salt in the given double batch. In the double batch, the ratio of garlic powder to salt is 8 tablespoons to 12 teaspoons. We can simplify this ratio by converting teaspoons to tablespoons. Since there are 3 teaspoons in a tablespoon, the ratio becomes 8 tablespoons to 4 tablespoons. This means that for every 4 tablespoons of salt, there are 8 tablespoons of garlic powder.
Now that we know the ratio, we can find out how much garlic powder is used with 18 teaspoons of salt. Since there are 3 teaspoons in a tablespoon, we divide 18 teaspoons by 3 to get 6 tablespoons of salt. Using the ratio, we can calculate the amount of garlic powder by multiplying the number of tablespoons of salt (6) by the ratio (8 tablespoons of garlic powder to 4 tablespoons of salt). This gives us 12 tablespoons of garlic powder.
Therefore, the answer is 12 tablespoons.