A soil sample was consolidated at a cell pressure of $20 \mathrm{kPa}$ and a back pressure of $10 \mathrm{kPa}$ for $24$ hours during a consolidated undrained $\text{(CU)}$ triaxial test. The cell pressure was increased to $30 \mathrm{kPa}$ on the next day and it resulted in the development of pore water pressure of $1 \mathrm{kPa}$. The soil sample failed when the axial stress was gradually increased to $50 \mathrm{kPa}$. The pore water pressure at failure was recorded as $21 \mathrm{kPa}$. The value of Skempton's pore pressure parameter $B$ for the soil sample is $\_\_\_\_\_\_\_$ (rounded off to $2$ decimal places).