The equilibrium temperature at 1 atmosphere pressure is 100 Dec. Any excess heat will be lost to evaporation.
Rough guess (SWAG) is delta T of 1.9 C of combined heat cap.
(5000g Cu )(0.1 cal/g C)(1.9 C)+(9000 g Water)(1.0 cal/g C)(1.9 C)= m(540 cal/g water)
Solve for m (mass of water evaporated)
Granted this is not the exact answer as it does not include the amount of water evaporated in the heat balance but it is correct to at least three significant digits, which is good enough for an engineer ( punch line of an old joke of the difference between an engineer, a physicists and a mathematician)