The time-of-day clock in AMA recorders increments every 6secondes. For an extremely brief telephone call, it is possible that the call answer entry and the call disconnect entry could have the same time stamp. Such a call would not be billed, even though it may have been completed. if a call lasts more than 6seconds, the two entries would have different time stamps and wouldbe billed. Sketch a graph that shows probability of billing on they axis and call duration on the x axis.