Robin has 1⁄2 cup of icing. She uses the same amount of icing to cover 18 cupcakes.
To find out how much icing she uses for each cupcake, we can divide the total amount of icing (1/2 cup) by the number of cupcakes:
1/2 cup / 18 cupcakes = 1/36 cup per cupcake
So, Robin uses 1/36 cup of icing to cover each cupcake.