A certain factory has one production line which includes $4-$stage process. And processing cost for each stage is as follow: K$1,$ K$2,$ K$3,$ K$4.$ And the processing cost increases $500$ VN$$ for next stage i$.$e$.$ K$2=$ K$1+500$; K$3=$ K$2+500$; K$4=$ K$3+500.$

In operations period of $10/2016,$ the report form factory manager is summarized such as: none final items, number of WIP at each stage: $110$ units, $160$ units, $210$ units, $280$ units respectively. The unit cost for material is $4,500$ VN$.$ In $10/2016,$ the total operational cost is $11,471,000$ VN$.$a$.$ Determine operational cost at each stage K$1,$ K$2,$ K$3,$ K$4(7$ points$)$