A rectаngulаr beаm has a crоss sectiоn оf b = 18 in., h = 24 in., and d = 21.5 in. It is reinforced with five No. 7 Grade 60 bars. The concrete strength is 5,500 psi (normal weight). The beam has Grade 60 No. 3 stirrups. Determine the assumed modulus of elasticity of the concrete, Ec.