An unknown material, m$1=0\mathrm{.}45$ kg$,$ at a temperature of T$1=81$ degrees C is added to a Dewer $($an insulated container$)$ which contains m$2=1\mathrm{.}9$ kg of water at T$2=21$degrees C$.$ Water has a specific heat of cw $=4186$ J$/($kg$$K$).$ After the system comes to equilibrium the final temperature is T $=30\mathrm{.}8$ degrees C$.$