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Q: Steel balls 12 mm in diameter are annealed by heating to 1150 K and then slowly cooling to 400 K in an air environment for which T8, = 325 K and h = 20 W/m2 · K. Assuming the properties of the steel to be k = 40 W/m · K, p = 7800 kg/m3, and c = 600J/kg · K, estimate the time required for the cooling process.