Question: Captopril is a drug designed to lower systolic blood pressure. When subjects were tested with this drug, their systolic blood pressure reading (in mm of mercury) were measured before and after the drug was taken, with the results given in the accompanying table.

a. Use the sample data to construct a 99% confidence interval for the mean difference between the before and after readings.

b. Is there sufficient evidence to support the claim that Captopril is effective in lowering systolic blood pressure?