Conversation so far:
What did James Black do?
James Black was an American knifemaker best known for his improvements to Bowie knife designed by Jim Bowie.
Why is the Bowie knife famous?
Jim Bowie had become famous for his use of a large knife at a duel known as the Sandbar Fight.

Question: How many knifes did he sold?
Self-contained rewrite: How many knives did James Black sell?