#### Answer

$\frac{10}{9}$ tons

#### Work Step by Step

$m=\frac{kwh^2}{l}$
Let $m$ be the weight of the beam.
Let $w$ be the width of the beam.
Let $h$ be the height of the beam.
Let $l$ be the length of the beam.
$m=3; w=\frac{1}{3}; h=1; l=10$
$3=\frac{k\frac{1}{3}(1)^2}{10}$
$3=\frac{k}{30}$
$3\times30=\frac{k}{30}\times30$
$k=90$
$m=\frac{90wh^2}{l}$
$w=1; h=\frac{1}{3}; l=9$
$m=\frac{90(1)(\frac{1}{3})^2}{9}$
$m=\frac{90}{81}$
$m=\frac{10}{9}$ tons