One recipe for pancakes says to use 1 1/2 cups of mix to make 7 pancakes. how much mix is needed to make 35 pancakes

The answer is 7 1/2 cups of mix.

If we need to have 3/4 cup of milk for a whole recipe
For half of it, we will multiply 3/4 by 1/2 to get the result.

3/4 x 1/2 = 3/8

To make half the recipe, we need only 3/8 of a cup of milk.
The information 1 cup of pancake mix is irrelevant because the question asks only about how much milk is needed.