Two students are assigned to work together on a project that requires both writing and an oral presentation. Steve can write $2$ or prepare $6$ of a presentation each day. Anna can write $4$ or prepare $2$ of a presentation each day.

a$.$ Who has a comparative advantage at writing?

b$.$ Suppose Steve goes to a writing tutor and learns some tricks that enable him to write $6$ each day. Now who has a comparative advantage at writing?