8.12 Office workers at a large organization are told that they should not work for more than one and a half hours at their PCs before taking a break. A survey of a random sample of 37 employees found that the mean time that they worked at their PCs before taking a break one morning was one hour 43 minutes with a standard deviation of 18 minutes. Test the hypothesis that on average the employees of this organization are working for no more than one and a half hours before taking a break using a 1 per cent level of significance.