You are called as an expert witness to analyze the fracture of a sintered silicon carbide plate that was fractured in bending when a blunt load was applied to the plate center. Measurement of the distance between the fracture origin and the mirror/mist boundary on the fracture surface gives a radius of 0.796 mm. You are given three pieces of the same SiC to test, and you determine that the mirror radius is 0.603, 0.203, and 0.162 mm for bending failure stress levels of 225, 368, and 442 MPa, respectively. What is your estimate of the stress present at the time of fracture for the original plate?