Answer
$$ y''= \frac{14}{25}x^{-12/5}.$$
Work Step by Step
Recall that $(x^n)'=nx^{n-1}$
Given $ y=x^{-2/5}$, then by using the power rule, we have
$$ y'=-\frac{2}{5}x^{-7/5},$$ and the second derivative $ y''$ is given by $$ y''=-\frac{2}{5}(-\frac{7}{5})x^{-12/5}=\frac{14}{25}x^{-12/5}.$$
