A gear reduction unit uses the countershaft shown in the figure below. Gear A receives power from another gear with the transmitted force F applied at the 20° pressure angle as shown. The power is transmitted through the shaft and delivered through gear B with a transmitted force F at the pressure angle shown. The gears A and B weigh 1000 N and 400 N respectively. The maximum tensile or compressive stress is not to exceed 70 MPa. Using Rankine's theory, determine the minimum diameter of the shaft, assuming fluctuating loads are absent.