An airline claims that 65% of its flights depart on time. A sample of 100 flights was examined and it was determined that 63% left on time. If the goal is to test whether less than 65% of the flights depart on time, what is the value of the calculated test statistic at the 5% level of significance?
a. z = -4.20 b. z = -0.42 c. z = 0.42 d. z = 4.20