Aunt bess uses 3 cups of oatmeal to bake 6 dozen cookies how many cups of oatmeal will she need to bake 18 dozen cookies

There are several important information's already given in the question. Based on those information's the answer to the question can be easily deduced.

Number of cups of Oatmeal

required by Aunt Bess for making 6 dozen cookies = 3

Then

Number of cups of oatmeal

required by Aunt Bess for making 1 dozen cookies = (3/6)

= 1/2

So

Number of cups of oatmeal

required by Aunt Bess for making 18 dozen cookies = (1/2) * 18

= 9 cups

So Aunt Bess will require 9 cups of oatmeal for baking 18 dozen cookies. I hope the procedure is clear enough for you to undestand.