Determine the percentage increase in heat transfer associated with attaching aluminum fins of rectangular profile to a plane wall. The fins are 50 mm long, 0.5 mm thick, and are equally spaced at a distance of 4 mm (250fins/m). The convection coefficient associated with the bare wall is 40 W/m2 ∙ K, while that resulting from attachment of the fins is 30 W/m2 ∙ K.