3mn,-5mn,8mn,-4mn

What is your question?

= 3 mb -5 mn +8mn -4mn

-2 mn+4 mn
2 mn

It seems like you have provided a sequence of numbers: 3mn, -5mn, 8mn, and -4mn. It is not clear what you would like to know about this sequence. Are you looking for the sum, the average, or any other specific information? Please provide more details so that I can assist you further.