For bronze:
$\sigma_{br} A_{br} = 2P$
$100(200) = 2P$
$P = 10\,000 \, \text{N}$
For aluminum:
$\sigma_{al} A_{al} = P$
$90(400) = P$
$P = 36\,000 \, \text{N}$
For Steel:
$\sigma_{st} A_{st} = 5P$
$P = 14\,000 \, \text{N}$
For safe value of P, use the smallest above. Thus,
$P = 10~000 \, \text{ N} = 10 \, \text{ kN}$ answer