$7\mathrm{.}15.$ Impulse$-$train sampling of x$[$n$]$ is used to obtain g$[$n$]=$ L x$[$n$]$S$[$n$-$ kN$].$ k$=-00$ If X$($ejw$)=0$ for $37$T$/7$ ::; lwl ::; $1$T$,$ determine the largest value for the sampling interval N which ensures that no aliasing takes place while sampling x$[$n$].$