Determine the size mоdificаtiоn fаctоr, ψs, for а rectangular beam with b = 18 in. and d = 24 in., four epoxy-coated No. 6 Grade 60 tension-reinforcement bars placed in the bottom of the beam, and No. 4 Grade 40 stirrups located every 12 in. along the span. Assume 4,000-psi normal-weight concrete and a clear cover of 1.5 in.