Pretzels are given away for free at a local store. The tray is constantly replenished as people take the pretzels.The number of pretzels in the tray is given by the function P(t) = 20 + t^2 − 8cosπt , where t is measured in minutes. When t = 1 minute, find the average rate of change of pretzels in the tray over the next 30 seconds.