A metal sphere of mass, m, at a temperature of 80∘C is placed into an equal mass of water at 20∘C in an insulated container. The specific heat capacity of water is twice that of the metal. After a short time, the metal and the water are at the same temperature. This new temperature is
a. 60∘C .
b. 50∘C .
c. 40∘C .
d. 30∘C .