A metal plate (k = 180 w/m·k, rho = 2800 kg/m³, and cp = 880 j/kg·k) with a thickness of 1 cm is being cooled by air at 5°c with a convection heat transfer coefficient of 30 w/m²·k. if the initial temperature of the plate is 300°c, determine the plate temperature gradient at the surface after 128 seconds of cooling. (round the final answer to one decimal place.)
The plate temperature gradient at the surface after 152 seconds of cooling is ___ K/m.