The answer is 3 and 1/3 cup of sugar, this is because it takes 2/3 of a cup to make 1 and a half dozen cookies (18 cookies).To get the answer you need to find out how many times 18 goes into 90 (5) and then multiply that number by the amount of sugar required to make 18 cookies (2/3 *5=3 and 1/3).
