$4-17.$ This problem re$-$examines the dirigible in Example $2-4.$ The balloon contains $5000$ moles of helium, which can be modeled as an ideal gas with $C_P^{**}=(\frac{5}{2})R$ at the conditions in this problem. The dirigible is initially at $T=25C$ and $P=1$atm. The dirigible flies slowly enough that all changes to the helium are reversible. Find $Q,W,U,H,$ and $S$ for the helium if its final state is:

A$.T=15C$ and $P=1$atm. Pressure is uniform throughout the process.

B$.T=25C$ and $P=0\mathrm{.}9$atm. Temperature is uniform throughout the process.