$6.$ An open channel has a trapezoidal cross section with a bottom width of $5\mathrm{.}6$ m and side slopes of $2$:$1($H:V$).$ If the normal depth of uniform flow is $2\mathrm{.}5$ m and the average velocity in the channel is $1\mathrm{.}3$ m$/$s$,$ calculate the discharge, and the freeboard in the channel. If the Manning coefficient for the channel is $0\mathrm{.}013,$ calculate the slope of the channel.