$(5)$ The brass rod AB and Aluminum rod BC are joined at the collar B and lightly fixed connected at their ends when T$\_1=15^$C$.$ The crosssectional area of each member is $1200$ mm$^2.$ If the temperature changes to T$\_2=50^$C$,$ determine: $($i$)$ the average normal stress in each member, and $($ii$)$ the final length of aluminum rod Use E$\_$br$=100$ GPa, E$\_$al$=75$ GPa, a$\_$br$=18^*10^-6/^$C$,$ a$\_$br$=18^*10^-6/^$C