Answer: Add all of the horizontal forces together, and add all of the vertical forces together.
Explanation:
An object is equilibrim when the net force acting on it equal equal zero.
Being force a vector, the net force is the vectorial sum of all the forces.
Also, being force a vector you can decompose each force into their vertical and horizontal components.
Since the sum of the vectors is made adding the corresponding components (vertical components to vertical components and horizontal components to horizontal components), the equlibrium of forces implies that the forces on every direction add up zero.
So, you add (always using the corresponding sign, positive or negative) all the horizontal forces together are the vertical forces together.
The forces are balanced If and only if the sum of the horizontal forces and the sum of the vertical forces are zero.