A drained triaxial compression test on a saturated clay yielded the effective shear strength parameters as $c’=15$ kPa and $\phi’=22^{\circ}$. Consolidated Undrained triaxial test on an identical sample of this clay at a cell pressure of $200$ kPa developed a pore water pressure of $150$ kPa at failure. The deviator stress (expressed in kPa) at failure is ________