I am unsure if I answered this questions correctly.
If A is a point with coordinates (-3,5,7) and point B has coordinates (-5,-4,9) then find displacement vector AB.
I got (-8,1,16), is this correct if not, what is the correct answer and how do you do it?
The coordinates of point $A$ has first component $-3$, and the coordinates of $B$ has first component $-5$. That means that to get from $A$ to $B$, you have to change the first component by $-2$. Thus the first coordinate of the displacement vector is $-2$.
Do the same for the two other components, and you have your answer. Remember to always go the same way (from $A$ to $B$), and you'll be fine.