7.
某厂生产某种产品的年固定成本为\(250\)万元,每生产\(x\)\((\)\(x\)\(∈N\)\({\,\!}^{*}\)\()\)千件,需另投入成本为\(C\)\((\)\(x\)\()\)万元,当年产量不足\(80\)千件时,\(C\)\((\)\(x\)\()\)\(=\)\( \dfrac{1}{3} \)\(x\)\({\,\!}^{2}\)\(+\)\(10\)\(x\)\((\)万元\();\)当年产量不少于\(80\)千件时,\(C\)\((\)\(x\)\()\)\(=\)\(51\)\(x+\)\( \dfrac{10000}{x} \)\(-\)\(1450(\)万元\()\).通过市场分析,当每件售价为\(500\)元时,该厂年内生产的商品能全部销售完.
\((1)\)写出年利润\(L\)\((\)单位:万元\()\)关于年产量\(x\)\((\)单位:千件\()\)的函数解析式\(;\)
\((2)\)年产量为多少千件时,该厂在这一商品的生产中所获利润最大\(?\)