If 45 cookies will serve 15 students, how many cookies are needed for 30 students?

I think i have it but not sure

Because your numbers are simple in this question, you can look at it this way ...

You know how many cookies are needed for 15 students but you need to fiqure out how many for 30 students. The ratio between 15 to 30 is a 1:2, AKA double. THis means that you can simply double the known number of cookies and it will give you the amount that you need for double the people.

Your answer is 90 cookies.