A machine element is subjected to the following bi-axial state of stress: $\sigma$x 80 MPa; $\sigma$y = 20MPa; $\tau$xy = 40 MPa. If the shear strength of the material is 100 MPa, the factor of safety as per Tresca’s maximum shear stress theory is
(a) 1.0 (b) 2.0
(c) 2.5 (d) 3.3