A thin walled tube with inner radius $c_1=120mm$ and outer radius $C_0=130mm$ is loaded by an axial force $P=180kN$ force passing through the centroid and a torque $T=8kNm$ as shown in Fig.Q$4.$

$($a$)$ Calculate the normal and shearing stresses at point A $.(6$ marks$)$

$($b$)$ Construct the Mohr circle for all the stress states at point $A.(6$ marks$)$

$($c$)$ Using Mohr's circle, determine the maximum normal stresses, and the maximum shear stresses and associated normal stress, as well as and their orientations at point $A.(8$ marks$)$