In the question there are numerous details given. Based on those details the result to the problem can be easily found.
The recipe for 2 dozen cookies require = 7 1/2 cups of flour.
= 15/2 cups of flour
Then
Amount of flour required to make 8 dozen cookies = [15/(2 * 2)] * 8
= (15/4) * 8
= 15 * 2
= 30
So 30 cups of flour are required to make 8 dozen cookies by following the same recipe.