Q$4.$ A sample of a soil failed in a triaxial test under a deviator stress of $200$kPa when the confining pressure was $100$kPa. If for the same sample, the confining pressure had been $200$kPa what would have been the deviator stress at failure in case $($a$)c=0($using both graphical and analytical method$)$ and $($b$){}_u=0($using graphical method$).$