The following data are given for a direct shear test conducted on dry silty sand.

specimen dimensions: $70$ mm by $70$ mm by $30$ mm $($height$)$

normal stress: $125$ kN$/$m$2$

shear force at failure: $250$ N

$($a$)$

Determine the angle of friction, $\backslash$phi $($in degrees$).$

$\_\backslash$deg

$($b$)$

For a normal stress of $180$ kN$/$m$2,$ what shear force $($in N$)$ is required to cause failure?

$\_$N