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 latex: t_{\infty}=325\: kt [infinity] = 325 k and latex: h=20\: \frac{w}{m^2k}h = 20 w m 2 k. assuming the properties of the steel to be k=40 w/m. k, and latex: \rho=7800\: \frac{kg}{m^3}rho = 7800 k g m 3, c= 600 j/kg. k, estimate the time required (in seconds) for the cooling process.