Answer:
It depends on where the arrow is showing / direction of the resultant force.
Add for vectors in same direction, ie., 5N + 4N=9N
(arrow pointing in same direction)
Minus for different directions, ie., 5N - 4N=1N
(arrow pointing in opposite direction)
Hope this helps!
Further examples:
6N 46N
--------> ----->
(6+4=10N)
5N 4N
<------------ ------>
(5-4=1N)
or
8N 6N
--------------> <--------
(8-6=2N)
