4. The state of stress of a particle of a body made from an isotropic, linearly elastic-ideally plastic material with a tied stress $\sigma_{yield} = 200$ MPa is given as
$\sigma = \begin{bmatrix} -60 & 40 & 0 \\ 40 & 80 & 0 \\ 0 & 0 & \sigma_{33} \end{bmatrix} MPa$
Compute the value of $\sigma_{33}$ required for yielding if the materials obeys:
1. Tresca Criteria
2. Von Mises Criteria