In a trend that scientists attribute, at least in part, to global warming, a certain floating cap of sea ice has been shrinking since 1980. The ice cap always shrinks in the summer and grows in winter. Average minimum size of the ice cap, in square miles, can be approximated by Upper A equals pi font size decreased by 5 r squared. In 2013, the radius of the ice cap was approximately 782 mi and was shrinking at a rate of approximately 4.2 mi divided by yr. How fast was the area changing at that time?