$($b$).$ Fig Q$4$ shows a piece of material subjected to a system of stresses. There are no stresses in the third mutually perpendicular plane $.$

$($i$)$ Determine by calculation the Principal stresses at the point and the inclination of the planes on which they act

$($ii$).$ Verify the results of $($i$)$ by means of Mohr stress circle.

$($iii$)$ Find the direct and shear stress on the Plane AB$.(17$ Marks$)$