(Solved): A hot-water stream at 80C enters a mixing chamber with a mass flow rate of 0.5kg/s where is is ...

A hot-water stream at $80^{?}\mathrm{C}$ enters a mixing chamber with a mass flow rate of $0.5\mathrm{kg}/\mathrm{s}$ where is is mixed with a stream of cold water at $20^{?}\mathrm{C}$. If it is desired that the mixture leave the chamber at $42{}^{?}\mathrm{C}$, determine the mass flow rate of the cold water stream. Assume all the streams are at the same pressure of $250\mathrm{kPa}$. A. $0.840\mathrm{kg}/\mathrm{s}$ B. $0.850\mathrm{kg}/\mathrm{s}$ C. $0.865\mathrm{kg}/\mathrm{s}$ D. $0.880\mathrm{kg}/\mathrm{s}$