Lets list what we know:
1.5 cups = 18 cookies
How many cups in 1 cookie will help us find the answer:
1.5 / 18 (1.5 cups per 18 cookies)
divide both sides by 1.5 (to get how many cookies in 1 cup)
1 / 12 (1 cup = 12 cookies)
Now, how many times does 12 fit in 30?
30/12 = 2.5
This means it takes 2 and a half cups of raisins to get 30 cookies.
If anything is still unclear please comment,
Hope this was helpful
Have a great day!