Hello! For 3 dozen muffins, you need 1½ cups of flour. When you divide 3/2 by 3, that's ½ cup of flour per dozen. To find the amount of flour needed for 5 dozen muffins, multiply the unit rate of flour needed per dozen (½) by the number of dozens needed. 1/2 * 5/1 is 5/2 or 2½ when simplified. 2½ cups of flour are required to make 5 dozen muffins.