Answer:
12 meters
Explanation:
The assumption regarding shadow lengths is that they are proportional to height at any given place and time.
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Here, the streetlamp is 9/6 = 3/2 times as tall as the tree, so we expect its shadow to be 3/2 times the length of the tree's shadow.
(3/2)(8 m) = 12 m
The streetlamp's shadow is 12 meters long.