$(40\%)$ A refrigeration cycle with the environmentally friendly refrigerant HFC$-134$a as the working fluid, as shown in the following figure. If the temperatures of Siate$\mathrm{.}1.($Saturated vapor$)$ and State $3($Saturated liquid$)$ are $-20C$ and $30C,$ respectively. $($a$)$ Calculate the temperature and pressures of States $2$ and $4.($b$)$ Please also evaluate the coefficient of performance $($C$.$O$.$P$.).$