Dawn sold 23% of the cookies
Since Tom sold 60% of 90 cookies and 60% of 90 is 54 and Scott sold 2/3 of 150 cookies, 2/3 of 150 is 100, and Dawn sold 46 of the cookies. All the numbers of cookies added (54+100+46) is 200. You then have to half the numbers to get the percentage, so you do 23 of 100 which is 23%, Dawn sold 23% of the cookies proven.