$4-7$ A piston$-$cylinder device initially contains $0\mathrm{.}07m^2$ of nitrogen gas at $130$ kPa and $180C.$ The nitrogen is now expanded to a pressure of $80$ kPa polytropically with a polytropic exponent whose value is equal to the specific heat ratio $($called isentropic expansion$).$ Determine the final temperature and the boundary work done during this process.