3. The amount of a particular biochemical substance related to bone breakdown was measured in 30 healthy women. The sample mean and standard deviation were 3.3 nanograms per milliliter (ng/mL) and 1.4 ng/mL. Construct an 80% confidence interval for the mean level of this substance in all healthy women. 4. A town council commissioned a random sample of 85 households to estimate the number of four-wheel vehicles per household in the town. The results are shown in the following frequency table. x|0 1 2 3 4 5 f|1 16 28 22 12 6 Construct a 98% confidence interval for the average number of four-wheel vehicles per household in the town.