This is the original force diagram,
To simplify the diagram, we can first cancel out the force which have opposite direction
The simplified diagram is the second picture in the left hand side.
To find the magnitudes and the direction of the combined force, we can use tip-to-tail method.
Since both force A and B are 3N in magnitudes and 60o between these two force,
so the dotted force is also 3N and have same direction with force C (equilateral triangle)
And the sum of these forces are 6N and direction OE