Clustering is especially useful in determining the relationship between ideas. You will be able to distinguish how the ideas fit together, especially where there is an abundance of ideas.
The word to be filled in this problem would be salary. Though you can use other words and/or phrases that would just fit in like a glove to complete the thought and make sense out of it. Since there is no particular instruction as to what is to be needed to be filled in there, then any word or words or phrases or even sentence fragments will do. As long as the thought is complete and that it makes sense when read, then there is no problem.
