implicit diff and related rates

Question

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 A=π r2. In​ 2013, the radius of the ice cap was approximately 787 mi and was shrinking at a rate of approximately 4.5 mi/yr.

How fast was the area changing at that​ time?

The area was changing at a rate of ___in 2013.

Answer 1