The answer is: 4.5 cups.
The explanation is shown below:
1. You need 3 cups of milk to make 30 biscuits.
2. Therefore, to solve the exercise you only need to multiply 45 biscuits by 3 cups and divide this by 30 biscuits.
3. Let's call the cups you will need to make 45 biscuits . Then, you have:
4. Therefore, you will need 4.5 cups to make 45 biscuits.