Answer
8 ft
Work Step by Step
Since the triangles are similar, the ratio of the lengths of the shadows is the same as the ratio of the heights of the objects.
Let s be the height of the sign.
$\frac{4.5}{12}=\frac{3}{s}\longrightarrow$ cross multiply to solve for s
$4.5s=36\longrightarrow$ divide each side by 4.5
$4.5s\div4.5=36\div4.5\longrightarrow$ divide
$s=8$
