To determine how many cups of frozen grapes Chandra needs to make 3 gallons of punch, we first need to convert gallons to cups and then find out how many recipes are required.
1 gallon = 16 cups, so 3 gallons = 3 × 16 = 48 cups.
Each recipe makes 6 cups of punch. Now, we find out how many recipes are needed to make 48 cups:
48 cups ÷ 6 cups/recipe = 8 recipes.
Now, according to the punch recipe, each recipe requires 1 cup of frozen grapes. If Chandra needs to make 8 recipes, she will need:
1 cup of frozen grapes/recipe × 8 recipes = 8 cups of frozen grapes.
Therefore, Chandra needs 8 cups of frozen grapes.