## Algebra: A Combined Approach (4th Edition)

$8$ feet
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