An object at a temperature of 80C to be cooled is placed in a refrigerator main- tained at 5C. It has been observed that the rate of temperature change of such an object is proportional to the surface area A and the difference between its temper- ature T and the temperature of the surrounding medium. Determine the time for the temperature to reach 8C if the constant of proportionality a = = 0.02 (s m m) -1 and A = 0.2 m.