2/3 cup flour makes 2 dozen cookies
since you want to make 8 dozen (hopefully not all for yourself !) then how many 2 dozens fit into 8 dozens ? 4 dozens
so since you multiply 2 by 4 to get 8, you will also multiply 2/3 by 4
2/3 * 4/1 = 8/3
you'll need 8/3 cups of flour. good luck on that cookie baking, make sure you dont burn anything !