Independence?

Classical Mechanics Level 3

Cold water at a temperature of $T_1$ is mixed with a sample of hot water at temperature $T_2$ . What physical factor is the final temperature of the mixture independent of? (Assume mixing occurs in an open system.)

The density of either the cold water or the hot water. The mass of either the cold water or the hot water. The external temperature at the time of mixing. The specific heat capacity of either the cold water or the hot water.