$33-5.$ A certain isotropic material yields in uniaxial tension at the stress ${}_Y=140$MPa,$At$ a

certain point in a structure made of this material, two of the three principal stresses are

$20$ MPa tensile and $90$ MPa compressive. If there is to be no yielding, what is the allow$-$

able range of the third principal stress according to $($a$)$ the maximum shear stress crite$-$

rion, and $($b$)$ the von Mises criterion?