4–109. The rigid beam is supported by the three posts A, B , and C . Posts A and C have a diameter of 60 mm and are made of a material for which E = 70 GPa and sY = 20 MPa. Post B is made of a material for which E_ = 100 GPa and sY_ = 590 MPa. If P = 130 kN , determine the diameter of post B so that all three posts are about to yield. (Do not assume that the three posts have equal uncompressed lengths.)