A $18-$mm thick $($B$)$ AISI $1020$ steel plate is sandwiched between two $13-$mm thick $($A$)2024-$t$3$ aluminum plates and compressed with a bolt and nut with no washers. The bolt is M$101\mathrm{.}5,$ property class $5\mathrm{.}8.$

a$)$ Find the suitable bolt length, rounded up to$$the nearest $5$ mm$.$

b$)$ Determine the bolt stiffness.$($You may enter your calculation using scientific notation.$)$

c$)$ Determine the material stiffness.