12 muffins - Cost of first Dozen: 12 * $4.50 = $54.00; Total cost = $54.00
13 muffins - Cost of first Dozen: (12 * $4.50 = $54.00) + (1 * $.25 = $.25)
Total cost = $54.25
14 muffins - Cost of first Dozen: (12 * $4.50 = $54.00) + (2 * $.25 = $.50)
Total cost = $54.50
15 muffins - Cost of first Dozen: (12 * $4.50 = $54.00) + (3 * $.25 = $.75)
Total cost = $54.75
16 muffins - Cost of first Dozen: (12 * $4.50 = $54.00) + (4 * $.25 = $1)
Total cost = $55