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.
For a parabola that opens upward, it must be a quadratic equation whose coefficient of x2 is a positive number.
So, I'll say x2+5x+6.
Equation is y=kx. We have four chance to figure out k; hopefully they all give the same result
x=9, y=63, y=kx becomes 63=k(9) so k=63/9=7
x=4, y=28, 28=k(4), k=7
The constant of proportionality is 7; we check 2×7=14, 11×7=77
Answer: k=7, y=7x
