$19\mathrm{.}55$ Use the conditions and processes of Problem $19\mathrm{.}54$ to$$compute $($a$)$ the work done by the gas, the heat added to it$,$ and its$$internal energy change during the initial expansion; $($b$)$ the work done, the heat added, and the internal energy change during the final cooling; $($c$)$ the internal energy change during the isothermal compression