$5-$ Following data are given for a direct shear test conducted on a dry sand: specimen diameter $=3$ inches

Normal force $=95lb$

Shear force at failure $=65lb$

a$)$ Determine the angle of friction, $\text{'}$

b$)$ For a normal stress of $20$ psi $,$ what shear force is required to bring the soil to failure? $(4$ points$)$

$\backslash$table$[[{}^{\text{'}}($deg$.),$Shear force $($lb$)],[,]]$