The rigid block has a weight of 80 kip and is to be supported by posts A and B, which are made of A-36 steel, and the post C, which is made of C83400 red brass. If all the posts have the same original lenth before they are loaded, determine the average normal stress developed in each post when post C is heated so that its temperature is increased by 20 degrees F. Each post has a cross-sectional area of 8 in2.