Physics - Temperature?

Question

In an insulated Styrofoam cup are mixed 0.59 kg of water at 23.48 °C and 0.13 kg of copper at 85.79 °C. Give the equilibrium temperature in °C.

Answer 1

Use Algebra!
The specific heat of liquid water: 4.1813 J/g•K
The specific heat of solid copper: 0.385 J/g•K
Let T°C be the equilibrium temperature. We have:
590*4.1813*(T-23.48) = 130*0.385*(85.79-T)
T = (130*0.385*85.79+590*4.1813*23.48)/(590*4.1813+130*0.385)
= 24.72 (°C) (answer)