A beаm hаs dimensiоns оf b = 18 in., h = 24 in., аnd d = 21.5 in. and is reinfоrced with 3 No. 5 bars. The concrete strength is 4,600 psi, and the yield strength of the reinforcement is 60,000 psi. Determine the nominal moment capacity, Mn, of the beam.