Refer to Exercise 7.S.6. Construct a 95% confidence interval for the population mean reduction in stem length. Does the confidence interval indicate whether the effect of stress is "horticulturally important," if "horticulturally important" is defined as a reduction in population mean stem length of at least
(a) 1 cm
(b) 2 cm
(c) 5 cm
Exercise 7.S.6
A plant physiologist conducted an experiment to determine whether mechanical stress can retard the growth of soybean plants. Young plants were randomly allocated to two groups of 13 plants each. Plants in one group were mechanically agitated by shaking for 20 minutes twice daily, while plants in the other group were not agitated. After 16 days of growth, the total stem length (cm) of each plant was measured, with the results given in the accompanying table.
Consider a t test to compare the treatments with the alternative hypothesis that stress tends to retard growth.

Control Stress rl 13 13 y 30.59 27.78 2.13 1.73