Calculate the unavailability of the following system. The load balancer switches cleanly between the presentation server and its backup. The presentation server uses the main database but can fail over to the database backup. The backup presentation server is only configured to use the main database, not its backup. LoadBalancer PresentationServerBackup PresentationServer Database DatabaseBackup Assume the following unavailabilities. Item Unavailability LoadBalancer 0.4% PresentationServer 1.5% PresentationServerBackup 1.8% Database 0.3% DatabaseBackup 0.4%