Answer
$v=0.80c$
Work Step by Step
We know that
$v=c\sqrt{1-(\frac{\Delta t_{\circ}}{\Delta t})^2}$
We plug in the known values to obtain:
$v=c\sqrt{1-(\frac{0.15\times 10^{-9}s}{0.25\times 10^{-9}s})^2}$
$v=0.80c$
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