$9-58.$ 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 C$83400$ red brass. If all the posts have the same original length 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 $20.$ Each post has a cross$-$sectional area of $8i{n}^2.$

Problem $9-58$