15. $\mathrm{X}$ is $\mathrm{N}\left(\mu_{1}, \sigma^{2} ight) $ and $\mathrm{Y}$ is $\mathrm{N}\left(\mu_{2}, \sigma^{2} ight)$ and let $\mathrm{Z}=\mathrm{X}+\mathrm{Y}$, then the distribution of $\mathrm{Z}$ is: $\mathrm{N}$ 16. For above $(Q$ 15), let $2=X$ - $y$ then the )Z distribution of $2$ is: SP.PC. 145