A 4-mm-diameter and 10-cm-long aluminum fin (k = 237 W/m-K) is attached to a surface at 300 C. If air is blown over the fin at 20 C with a heat transfer coefficient of 12 W/m2 -K, is the infinite fin assumption valid? Must prove mathematically!! (Ac = 1.26 x 10-5 m2 , P = 0.0126 m)