A Freon$-12$ refrigerating machine operates on the ideal vapour compression cycle

between the limits $-15C$ and $25C.$ The vapour is dry saturated at the end of

isentropic compression and there is no undercooling of the condensate in the

condenser. Calculate $($a$)$ the dryness fraction at the suction of the compressor, $($b$)$

the refrigerating effect per kg of refrigerant, $($c$)$ the coefficient of performance, $($d$)$

the cannot coefficient of performance.