A cylindrical steel rod, 0.01 m in diameter and 0.2 m in length is first heated to 7500c and then immmersed in a water both at 1000C. The heat transfer coefficient is 250 W/m2-K. The density, specific heat and thermal conductivity of steel are r = 7801 kg/m3, c = 473 J/kg-K, and k = 43 W/m-K, respectively. The time required for the rod to reach 3000C is ________ seconds.