3. The height of oak seedlings sixteen months after planting is normally distributed with population mean = 16 inches and population standard deviation = 4 inches. What proportion of the individual oak seedlings are between 9 to 21 inches high?

4. Lead is a dangerous toxin and people's exposure to lead should be minimized. A public health researcher wants to estimate the amount of lead in bread wrappers. Assume that the population mean = 30 milligrams and population standard deviation = 5 milligrams. Find Q3 (the 75th percentile) for the amount of lead in bread wrappers.