A treatment plant that sends effluent into the river claims the mean suspended solids

is never above 40 mg/l. Measurements of the suspended solids in river water on n = 14 Monday mornings yield sample mean as 46 and sample standard deviation 9.4 mg/l. Based on data collected over a period of many years, it is reasonable to assume that the individual

measurements follow a normal distribution. Calculate the value of t correct to 3 decimal places.