Thermodynamics, heat in a copper cube transfer to water

[thereddevils]

Homework Statement

When a copper cube of side of 2.0 cm is immersed into a perfectly insulated container filled with 1.0 kg of water at 5 degree celcius , the temperature of water rises to 7 degree celcius . Assuming that no heat is lost to the surrounding , calculate the original temperature of the cube .

Given density of copper = 8900 kg / m^3 , specific heat capacity of water = 4180 J/kg/K and specific heat capacity of copper = 385 J/kg/K

Homework Equations

The Attempt at a Solution

from Q=mc theta = 1(4180)(2) = 8360 J and this is the heat supplied to the water

mass of copper = (8900)(8 x 10^(-6)) = 0.0712 kg

8360=0.0712(385) d theta

d theta = 305 degree celcius but this is the change in temperature , how do i find the original temperature from there .

 

[rl.bhat]

Final temperature of the mixture is 7 degrees
Change in temperature = Original temperature of the copper - final temperature of the mixture.