dolution

Environmentalists are concerned about emissions of sulphur dioxide into the air. The average number of days per year in which sulphur dioxide levels exceed 150 milligrams per cubic metre in Milan, Italy, is 29. The number of days per year in which emission limits are exceeded is normally distributed with a standard deviation of 4.0 days. What percentage of the years would average between 21 and 37 days of excess emissions of sulphur dioxide? What percentage of the years would exceed 37 days? What percentage of the years would exceed 41 days? In what percentage of the years would there be fewer than 25 days with excess sulphur dioxide emissions?