A hot water stream at 75oC enters a mixing chamber with a mass flow rate of 1

Question:

A hot water stream at 75oC enters a mixing chamber with a mass flow rate of 1 kg/s where it is mixed with a stream of cold water at 15oC. If it is desired that the mixture leaves the chamber at 40oC, determine
(a) The mass flow rate of cold water stream.
(b) The entropy generation rate during mixing. Assume all streams are at a pressure of 300 kPa.