A plane surface is provided with an array of straight rectangular fins of thickness and length 1.5 mm and 25 mm respectively. The fins are spaced on a 3.5 mm pitch. The fins are made of a material with a thermal conductivity of 100 W/mK, and the heat transfer coefficient at all exposed surfaces is 300 W/m2 K. If the fin base temperature is 95∘C and the ambient fluid is 25 ∘ C, find the overall surface efficiency of the array and the heat transferred to the fluid per square metre of primary surface.