Select the number and size of reinforcing bars required to resist a total factored moment of 180 ft. kips for a rectangular section with b = 12 in., d = 19.5 in., h = 24 in., fc = 4 ksi, and fy = 60 ksi. Check for minimum reinforcement requirement. Use the three methods:
1. Solve the quadratic equation in As
2. Use the approximate lever arm (d-a/2) method
3. Use the design chart for R