Q$2)-(6$ marks$)$ The weights, in decagrams, of a sample of $10$ packages of grass seed distributed by a certain company: yielded a sample mean of $46\mathrm{.}12$ and a variance of $0\mathrm{.}286.$ Find a $85\%$ confidence interval for the true standard deviation of the weights of all such packages of grass seed distributed by this company, assuming a normal population.