As seen in Fig. P6.6, a stepped shaft ABC with built-in end at A is subjected to the tor...

As seen in Fig. P6.6, a stepped shaft ABC with built-in end at A is subjected to the torques T_B=3 kN.m and T_C=1 kN.m at sections B and C. Based on a stress concentration factor K = 1.6 at the step B, what is the maximum shearing stress in the shaft? Given: d₁ = 50 mm and d₂ = 40 mm.