4. An owner of a local gas station wants to know the proportion of customers who use her pay-at- the-pump feature. This feature allows customers to use a credit card at the pump and never enter the station. She surveyed 200 customers and found that 150 used the pay-at-the-pump feature. a. What is the sample proportion of people who use the pay-at-the-pump feature? b. Suppose she wants to create a confidence level using the 90% level of confidence. What is the value of z? c. What is the lower bound of the confidence interval? d. What is the upper bound of the confidence interval? e. Would it be reasonable to conclude that the population proportion is 0.78