16. In the figure below, the numbers labeled at 8 vertices: $a, b, c, d, e, f, g, h$, each of these numbers is equal to $1/3$ of the sum of the numbers at the three adjacent vertices. Find: $(a+b+c+d)-(e+f+g+h)$.

 untranslated part:
 
将上面的文本翻译成英文，请保留源文本的换行和格式，直接输出翻译结果。 

Note: The last sentence is a note and not part of the problem statement, so it is not translated.