$($a$)$ A direct shear $($shear box$)$ test carried out on three specimens of the

same clay soil yielded the following results:

Determine the values of the shear strength parameters $c^{\text{'}}$ and ${}^{\text{'}}.$

$($b$)$ A series of unconsolidated$-$undrained triaxial tests were carried out on

specimens of the same fully saturated sandy clay. The following results

were obtained at failure:

Determine the values of the shear strength parameters $c_u$ and ${}_u.$