Happy-to-Help.CA, an online pharmacy, promises to deliver prescriptions to its customers for free. Online consultations with their pharmacists and doctors are also offered. Recently, the company's internal audit department selected a random sample of 40 prescriptions issued throughout the system. The objective of the sampling was to estimate the average dollar value of all prescriptions issued by the company. The sampling resulted in a sample mean of $57.65 and the standard deviation of $10.50. Use this sample information to find a 90% confidence interval for the true average sales value for prescriptions issued by Happy-to-Help. CA. Assume that the values are approximately normally distributed and use the t distribution. (a) What is df (degrees of freedom) in this case? df = For part (b), round your answer to 3 decimal places. (b) Find to = For part (c), round your answers to 2 decimal places. (b) What is the 90% confidence interval for the true average sales value for prescriptions issued by Happy- to-Help.CA