$6$ It costs $\backslash (\backslash$$ $40\backslash )$ to buy a telephone from the department store. Assume that I can keep a telephone for at most five years and that the estimated maintenance cost each year of operation is as follows: year $\backslash (1,\backslash$$ $20\backslash )$; year $\backslash (2,\backslash$$ $30\backslash )$; year $3,\backslash (\backslash$$ $40\backslash )$; year $\backslash (4,\backslash$$ $60\backslash )$; year $5,\backslash (\backslash$$ $70\backslash ).$ I have just purchased a new telephone. Assuming that a telephone has no salvage value, determine how to minimize the total cost of purchasing and operating a telephone for the next six years.Please use shortpath