Two $150$ mm x $75$ mm x $4$ m long timber members are reinforced with a steel

plate $150$ mm $6$ mm x $4$ m long, the three members being adequately bolted

together. The permissible stresses for the timber and the steel are $6$ N$/$mm$2$

and $130$ N$/$mm$2,$ respectively and E for timber is $8200$ N$/$mm$2$ and for steel E

is $205000$ N$/$mm$2.$ Calculate:

a$)$ the permissible tensile load for this composite member and

b$)$ the amount of elongation due to this load.