Outflow is the answer assuming that the underlined word is influx.
Answer:
by explaining how a captive’s condition was assessed.
Explanation:
The author developed the central idea that transporting enslaved captives was a trade just like any other in "Captain Canot" or "Twenty Years of an African Slaver" by explaining how a captive’s condition was assessed.
Most trades or all trades have profit as its main driving force, and profit cannot be made if the goods you sell is not good enough, so slave masters had to assess a captive's condition to find out if he was good enough to make a profit or not just like any other trade.
