The original recipe is for 36 muffins, they want to make 12:
Find the ratio:
12/36 = 1/3
They would need 1/3 of the recipe, so you would divide all the ingredients by 3.
Flour: 5 1/4 cups = 21/4 cups
21/4 / 3 = 21/12 = 1 3/4 cups.
Oil: 1 cup / 3 = 1/3 cup
Baking powder: 4 1/2 = 9/2
9/2 / 3 = 9/6 = 1 1/2 teaspoons
salt: 1 1/2 = 3/2
3/2 / 3 = 3/6 = 1/2 teaspoons
eggs 3 / 1 = 1 egg
Nutmeg: 1 1/2 = 3/2
3/2 / 3 = 1/2 teaspoons
cinnamon: 3/4 / 3 = 1/4 teaspoon
The amount of sugar and milk aren't listed but just divide those by 3 to find the amount needed.