solve a to c please

Problem $6\mathrm{.}15$ CU triaxial compression tests were performed on two samples of a clayey soil containing $60\%$ kaolinite and $5\%$ illite. The preconsolidation pressure for this soil was determined to be equal to $500$ kPa. Additional information about the soil includes: Gs $=2\mathrm{.}63$; smectite content ; nonclay material mostly composed of quartz and

other silicates; and void ratio $=1\mathrm{.}021\mathrm{.}07.$ One sample was isotropically consolidated to $125$ kPa; the other, to $313$ kPa before shearing. The results of the shearing stage of the test are shown in P$-$Figure $6\mathrm{.}5$ and P$-$Table $6\mathrm{.}4.($a$)$ Determine the OCR for each sample. $($b$)$ Determine the undrained shear strength su$.($c$)$ Estimate the critical$-$state friction angle of this soil.