Conversation so far:
What is Marie Stopes' Married Love?
Married Love or Love in Marriage is a book by British academic Marie Stopes.
What was Marie Stopes' marriage book called?
Married Love or Love in Marriage is the title of the book by British academic Marie Stopes.

Question: how many copies did it sell?
Self-contained rewrite: How many copies did Marie Stopes' Married Love or Love in Marriage book sell?