A Plane Stress Element on a Bar in Uniaxial Stress $\sigma_{\theta}=78 \mathrm{MPa}$

A plane stress element on a bar in uniaxial stress has a tensile stress of $\sigma_{\theta}=78 \mathrm{MPa}$ (see fig.). The maximum shear stress in the bar is
Approximately: (A) $29 \mathrm{MPa}$
(B) $37 \mathrm{MPa}$
(C) $50 \mathrm{MPa}$
(D) $59 \mathrm{MPa}$