Answer
$2r^2\pi+2\frac{100}{r}$
Work Step by Step
We know that the surface of a cylinder can be obtained by: $S=2r^2\pi+2\pi rl$, from part a): $l=\frac{100}{r^2\pi}$, hence: $S=2r^2\pi+2\pi r\frac{100}{r^2\pi}=2r^2\pi+2\frac{100}{r}$
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