18. 3 cups of water, convert it to pints:
To make a double recipe she needs to use 2 pints of water.
Then, the 3 cups of water Cheryl has measured are not enought for a double recipe.
19. The recipe uses 1/2 cup of cornstarch
To make 15 time the recipe the amount of cornstarch is:
Convert the 7.5cups to tablespoons:
Then, to make 15 times the recipe Cheryl needs to use 120 tablespoons of cornstarch