An RCC beam of rectangular cross section has factored shear of $200$ kN at its critical section. Its width $b$ is $250$ mm and effective depth $d$ is $350$ mm. Assume design shear strength $\tau_c$ of concrete as $0.62 \: N/mm^2$ and maximum allowable shear stress $\tau_{c,max}$ in concrete as $2.8 N/mm^2$. If two legged $10$ mm diameter vertical stirrups of $\text{Fe}250$ grade steel are used, then the required spacing (in cm, up to one decimal place) as per limit state method will be _____