Answer:
Step-by-step explanation:
Source A is useful as a first-hand account of what happened to the slaves when they were captured. This is slightly more useful as an insight into their actual lives because it comes from somebody who witnessed it.
Source B is useful in more of a numeric way, as the diagram shows how many slaves were inside of ships and how they would have been 'stowed'. This is still useful, but not as much as a first-hand account because the diagram is drawn from an outsider's point of view.