4. The state of stress at a point is σ₁ = 140 MPa, σ₁ = -220 MPa, σ₂ = 160 MPa, Txy = -80 MPa, Tyz = 100 MPa,
Txz = -120 MPa. [Answers: 301.72 MPa, 29.83 MPa, -251.55 MPa, max shear = 276.6 MPa]
a. Calculate the principal stresses.
b. Draw the 3D Mohr's circle for the state of stress.
c. Calculate the maximum shear stress.