#### Answer

$8$ feet

#### Work Step by Step

Let $I$ be the intensity of light.
$I=\frac{k}{x^2}$
$I=80; x=2$
$80=\frac{k}{(2)^2}$
$k=320$
$I=\frac{320}{x^2}$
$I=5$
$5=\frac{320}{x^2}$
$x^2=\frac{320}{5}$
$x^2=64$
$x=8$ feet

Published by
Pearson

ISBN 10:
0321726391

ISBN 13:
978-0-32172-639-1

$8$ feet

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