The effectiveness of a blood-pressure drug is being investigated. An experimenter finds that, on average, the reduction in systolic blood pressure is 31.3 for a sample of size 21 and standard deviation 13.7. Estimate how much the drug will lower a typical patient's systolic blood pressure (using a 80% confidence level).Assume the data is from a normally distributed population.

Enter your answer as a tri-linear inequality accurate to three decimal places.