3. If the random variable $X$ is distributed as $N(\mu, \delta^2)$ and $0 < p < 1$. Show that the $p_{th}$ quantile of X is given by: $x_p = \mu + \delta \cdot \Phi^{-1}(p)$, where the $\Phi(x)$ is the cumulative distribution function of a standard normal random variable. (10 分)