2-stage cascade refrigeration system supplies 20 tons of refrigeration at evaporator temperature of -50 C. The load at -50 C is absorbed by a unit using R-22 and heat is rejected to cascade condenser at -10 C. The cascade condenser is cooled by a unit using R-12 with evaporator temperature of -25 C and condenser temperature of 40 C. Liquid R-12 is sub-cooled by 5 C before expansion. Assuming the refrigerants leaving both the evaporators are dry saturated, isentropic compression, and no other losses, find (i) Compression ratios of both units (ii) Mass of both refrigerants, (iii) COP of each unit, (iv) COP of the System (v) power required