Answer
See below.
Work Step by Step
By the text of the exercise $S(r)=S(r(t))=S(t)=4\pi r^2=4\pi r^2(t)=4\pi (\frac{2}{3}t^3)^2=4\pi \frac{4}{9}t^6=\frac{16\pi}{9}t^6$
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