$(50)2.$ Consider the truss shown made of Aluminum $(E=71$GPa $).$ The truss members are square

tubes with cross section external and internal dimensions of $30$ mm and $20$ mm $,$

respectively. Determine

$($a$)$ the element stiffness matrices

$($b$)$ the global stiffness matrix

$($c$)$ the nodal deflections

$($d$)$ the axial force in the horizontal member

$($e$)$ the stress in the horizontal member.