Hot gas inside an internal combustion engine of a car expands in a reversible manner during the expansion stroke to turn the shaft and move the vehicle forward. The gas was at 800 K and 4 MPa at the start, and expands until reaching 0.5 MPa pressure. The expansion ratio (i.e. the ratio of the final volume to the initial volume) is 4.0. Assume the gas to be air, and assume it to behave like an ideal gas. Calculate the final temperature of the gas and change in entropy per unit mass during this expansion.