There are two structural weakness planes emanating from the corners of the sidewall of the opening. The inclinations of the discontinuities are $\backslash (60^\{\backslash$circ$\}\backslash )$ and $\backslash (120^\{\backslash$circ$\}\backslash )$ respectively. The unit weight of the rock is $\backslash (41\backslash$mathrm$\{$kN$\}/\backslash$mathrm$\{$m$\}^\{3\}\backslash ),$ and the height of the opening is $9\mathrm{.}9$ m $.$ Determine the total support force per metre length of opening required to prevent sliding of the rock in the sidewall in kN$/$m$.$