Water and ice having equal masses are placed inside an insulated container. The initial temperatures of water and ice are 40^ C and 0^ C respectively. The equilibrium temperature of the system in degrees Celsius is close to (Note: take the specific heat of water =4000 ~J ~kg ⁻¹ ~K ⁻¹ ; latent heat of fusion =300 ~kJ ~kg ⁻¹ )