A simple beam has a 24 foot span and a W16 X 50 section. Determine the maximum flexural stress due to two concentrated loads, both 20 kips, at the 1/3 point and the 2/3 point (8 feet and 16 feet) on the beam. For this section d = 16.26 in, I = 659 in^4, and S = 81 in^3.