$(30$pt$)$ It costs $$40$ to buy a telephone from the department store. Assume that I can keep a telephone for at most four years and that the estimated maintenance cost each year of operation is as follows: year $1,$ $$20$; year $2,$ $$30$; year $3,$ $$40$; year $4,$ $$60.$ I have just purchased a new telephone. Assume that a telephone has no salvage value. Draw the network model that is node $1$ for the beginning of year $1$ and node $6$ for the end of year $5.$ Determine how to minimize the total cost of purchasing and operating a telephone for the next five years with Dijkstra's Algorithm. There will be two alternative ways, please show both of them.