HW $9(2)-4$: $(8$ points$)$

Refrigerant$-134$a is converted from a saturated liquid to a saturated vapor in a closed system using a reversible constant pressure process by transferring heat from a heat reservoir at $6C.$ Take $T_0=25C$ and $P_0=100$kPa. Calculate the useful work per unit mass $(w_u)$ and the exergy destroyed per unit mass $(x_{\text{d}\text{e}\text{s}})$ at:

$($a$)P^{\text{'}}=100$kPa.,$(4pt)$

$($b$)P^{\text{'}\text{'}}=180$kPa. $(4$ pt$)$

$($Write down your calculation steps$)$