Proh, $$\mathrm{.}6-12,$ The rectarical system of Iig. P$3\mathrm{.}6-13$ eonsists of a "rizid" beam AAC and two idestical ASTM A$-35$ whel hars wich crows$-$uctional area $A=1\mathrm{.}2i{n}^2-($Fur $F$ and a$,$ see Tables F$\mathrm{.}2$ and A$3.)$ The bean is apported by a at A and $C.$ After the pins have been iaseried at A and $C,$ the imo hars are stres Iree. $($a$)$ Usigg the dinencions listed helow, devernize the asial dresses inductd in lars $(1)$ and $(2)$ if the iemperatuet of bar $($a$)$ is decrensed by $507.($b$)$ Desernire the $($small$)$ angle a strough which the beam AC would reate due ta this temperabure changz $($c$)$ Re$-$anle Part $($a$)$ if the crosp$-$sectional area of kor $($i$)$ is doukled to $A_1=24$ in ${?}^2,$ utile the crostsectional area of bar $(2)$ renains uechinged.

$a=20in,L_1=L_{-2}=20in.$