Problem $\backslash$#$1(60$ points$)$

Three soil elements are shown below. For each soil element, determine the following parameters using BOTH equations and Mohr's circles:

$(1)$ Major and minor principal stresses

$(2)$ Normal and shear stresses on plane $\backslash ($ A B $\backslash )$

Note that when using the Mohr's circle approach, Mohr's circles need to be drawn using a software or compass to scale. Points will be deducted for hand$-$drawn Mohr's circles.

$($a$)$