In a test of effectiveness of garlic for lowering cholesterol, 50 subjects were treated with raw garlic. Cholesterol levels were measured before and after the treatment. The changes in their levels of LDL cholesterol in (mg/dL) has a mean of 0.5 and a standard deviation of 22.0. Construct a 95% confidence interval estimate of the standard deviation of the changes in LDL cholesterol after the garlic treatment. Assume that the sample is a simple random sample obtained from a population with a normal distribution.