To determine how many servings can be made from 4 cups of milk, we start with the original recipe information. The recipe uses 3 cups of milk to make 9 servings.
First, we find out how many servings can be made per cup of milk:
\[ \text{Servings per cup} = \frac{9 \text{ servings}}{3 \text{ cups}} = 3 \text{ servings per cup} \]
Now, we can calculate how many servings can be made from 4 cups:
\[ \text{Total servings from 4 cups} = 4 \text{ cups} \times 3 \text{ servings per cup} = 12 \text{ servings} \]
Therefore, you can make 12 servings from 4 cups of milk.