A combined rectangular footing is shown below. Effective depth $=600mm,f^{\text{'}}c=27\mathrm{.}5$ MPa, fy $=413$MPa. Net soil pressure at factored loads, qu $=98$kPa. Reduction factors: $=0\mathrm{.}75$ for shear, $=0\mathrm{.}90$ for moment

$-610\mathrm{.}4$

Determine the critical wide beam shear stress $($MPa$).$