Answer
$1.39\times10^{-3}\,s$
Work Step by Step
$V=V_{0}\sin 2\pi ft$
Given that $f=60.0\,Hz$ and $V=\frac{V_{0}}{2}$
$\implies \sin 2\pi ft=\frac{1}{2}$
Or $\sin 120\pi t=\frac{1}{2}$
Or $\sin^{-1}\frac{1}{2}=120\pi t$
That is, $\frac{\pi}{6}=120\pi t$
$t=\frac{1}{6\times120}=\frac{x}{y}=1.39\times10^{-3}\,s$
