A 30-cm-long, 1-cm-diameter aluminium fin (k=237 W/m·K) is exposed to an environment at 22oC. The base temperature of the fin is maintained at 80 oC. The heat transfer coefficient between the rod and the surrounding air is 11 W/m2·K. If the fin can be assumed to be very long, (a) determine the efficiency of a single fin (ηs). (b) If 100 of such fins form a 10 x 10 fin array on 21 cm x 21 cm base plate surface, determine the overall surface efficiency (ηo).