Answer
$v = 400~m/s$
Work Step by Step
The image shows the standing wave pattern for the second harmonic.
We can find the speed of sound in the tube as:
$v = f_2~\lambda_2$
$v = (f_2)~(\frac{2L}{2})$
$v = (500~Hz)(0.80~m)$
$v = 400~m/s$
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