Answer: 1-4/5 dozens of muffins.
Step-by-step explanation;
Step One. Turn the fractions into decimals to make it easier; 4-1/2 will be 4.5 and 2-1/2 will be 2.5.
Step Two. Apply the rule of three, using the variable x to represent the number of muffins Garnet can make; 2.5/1 = 4.5/x.
Step Three. Solve for x by cross multiplying; x = 1.8. So Garnet can make 1.8 dozens of muffins with 4.5 cups of flour.
Step Four. Convert the decimal into a fraction; 1.8 in a fraction form is 9/5, or 1-4/5.