Answer:
a) 1/6 cup
Explanation:
A bread recipe calls for 1/3 cup of butter. If you only want to make 1/2 of a batch you would need to use one half of the ingredients used in the original recipe.
So, if you originally need 1/3 cup of butter, you'd need to use half of it.
We are going to solve it like this:

Thus, you'd need 1/6 cup of butter to make 1/2 of a batch.