Historical data show that customers who download music from a

Historical data show that customers who download music from a popular Web service spend approximately ​$21 per​ month, with a standard deviation of ​$3. Assume the spending follows the normal probability distribution. Find the probability that a customer will spend at least ​$17 per month. How much​ (or more) do the top ​11% of customers​ spend? What is the probability that a customer will spend at least ​$17 per​ month?