Captopril is a drug designed to lower systolic blood pressure. When subjects were tested with this drug, their systolic blood pressure readings (in millimeters 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?

Based on data from "Essential Hypertension: Effect of an Oral Inhibitor of Angiotensin-Converting Enzyme" by MacGregor et al., British Medical Journal, Vol. 2.

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Subject A B CDEFGHIK L Before 200 174 198 170 179 182 193 209 185 155 169 210 After 191 170 177 167 159 151 176 183 59 145 146 177