(3) (Minimizing average completion-time) (30 points) Suppose you are given a col- lection of n tasks that need to be scheduled. With each task, you are given its duration Specifically, task i takes ti units of time to execute, and can be started at any time. At any moment, only one task can be scheduled The problem is to determine how to schedule the tasks so as to minimize their average completion-time. More precisely, if ci is the time at which task i completes in a particular schedule, the average completion-time for the schedule is