When all the individual forces acting upon an object are balanced, then the object is at equilibrium. When a force is at an angle to the traditional x-y axes, it is customary to consider the components of the force in the analysis. The components of a force vector are the projections of that vector onto the x- and the y-axis. By thinking in terms of components, it is considerably easier to determine what forces would be required to bring an object to equilibrium.
 

"Reading" the Diagram
In this problem, you want to balance the given force by adding two forces to the object. The given force is an angled force. Like all angled forces, it has an x- and a y-component. Since the force is drawn on a background grid of squares that represent 10 N along each edge, it is easy to determine the x- and the y-components.  For instance, an angled force vector that stretches horizontally for 7 squares has an x-component of 70 N.  If the same angled vector stretches vertically across 4 squares, then the y-component is 40 N. Begin this problem by determining the x- and the y-component of the given force.


Balance the Forces
If the given force has an x-component of 70 N to the west (left on the diagram), then you need to add an equal strength force in the opposite direction. That is the only way that you can balance the given force. So add a force of 70 N to the east. By the same reasoning, you will have to add a vertical force to balance the given force's y-component. So if the y-component is 40 N to the north (upward on the diagram), then add a 40 N force directed southward.