From a statistical analysis of their past projects, ShellLock Construction Corporation has determined that the mean and variance of their construction mobilization periods is 25 and 4 days, respectively. During a recent internal audit of the company's operations, 10 past construction projects were sampled at random. Find the 90% confidence interval for the mobilization periods of ShellLock's past construction projects. Assume that the population (i.e., mobilization periods of all past projects) is normally distributed.