MLA format question about in-text citation with multiple works, same author?

I have an MLA formatted paper that has both a book and an essay by the same author. I'm having difficulty with my in-text citation and can use a little help. The book and essay are Chinua Achebe's Things Fall Apart, and the essay is An image of Africa:Racism in Conrad's Heart of Darkness. Would the book be quoted as (Things, 38) or just (38) or (Achebe 38) if I have mentioned the author by name? Also If I have not mentioned the essay or author by name would it be (An image of, Achebe 22)