3. (15 points) Suppose the amount of heating oil used annually by households in Iowa is normally distributed with mean 200 gallons per household per year and a standard deviation of 40 gallons of heating oil per household per year. (a) (9 points) Find the probability of a randomly selected household in Iowa using more than 150 gallons of heating oil per year. A complete formula will suffice (b) (6 points) Is it unusual for a household in Iowa to use 250 gallons of heating oil per year? Explain