A rectаngulаr beаm has a crоss sectiоn оf b = 18 in., h = 30 in., and d = 27.5 in. It is reinforced with five No. 5 Grade 60 bars. The concrete strength is 8,500 psi (normal weight). The beam has Grade 60 No. 3 stirrups. Determine the assumed modulus of elasticity of the concrete, Ec.