Historical data show that customers who download music from a popular Web service spend approximately $20 per month, with a standard deviation of $4. Assume the spending folcws the normal probability distribution. Find the probability that a customer will spend at least $16 per month. How much (or more) do the top 12% at customers spend? What is the probability that a customer will spend at least $1 5 per month? D (Round to four decimal places as needed)