Extracted text: A sign for an automobile service station is supported by two aluminum poles of hollow circular cross section, as shown in the figure. The poles are being designed to resist a wind pressure of 3.2 kPa against the full area of the sign. The dimensions of the poles and sign are hi = 16.0 m, h2 = 4.0 m, and b = 8.0 m. To prevent buckling of the walls of the poles, the thickness t is specified as one tenth the outside diameter d. Wind load P (a) Determine the minimum required diameter of the poles based upon an allowable bending stress of 45 MPa in the aluminum. Round to the nearest whole number. d = mm (b) Determine the minimum required diameter based upon an allowable shear stress of 13 MPa. Round to one decimal place. d = mm