A 98.0°C piece of cadmium (c=.850J/g°C) is placed in 150.0g of 37.0°C water. After sitting for a few minutes, both have a temperature of 38.6°C. What was the mass of the cadmium sample?

• zoexoe: The answer is 19.9 grams cadmium. 
  Assuming there was no heat leaked from the system, the heat q lost by cadmium would be equal to the heat gained by the water:
       heat lost by cadmium = heat gained by the water
       -qcadmium = qwater
  Since q is equal to mcΔT, we can now calculate for the mass m of the cadmium sample:
       -qcadmium = qwater
       -(mcadmium)(0.850J/g°C)(38.6°C-98.0°C)) = 150.0g(4.18J/g°C)(38.6°C-37.0°C)
       mcadmium = 19.9 grams