A two-stage cascade refrigeration system is to provide cooling at -40oC while operating the high-temperature condenser at 1.6 MPa. Each stage operates on the ideal vapor-compression refrigeration cycle. The upper vapor compression refrigeration system (VCRS) uses water as its working fluid and operates its condenser at 400 kPa. This system produces a cooling effect of 20 kJ/s. Determine the mass flow rate of R-134a and water in their respective cycles, and the overall COP of this cascaded system.