SHANGHAI — China's biggest steelmaker, Shanghai Baogang Group Co., plans to lay off 40,000 employees, responding to the nation's slowing economic growth. Baosteel has a workforce of 130,000 and plans to cut it by almost a third in three years. The city of Shanghai will suffer 226,000 total layoffs this year as the central government attempts to trim payrolls and eliminate unwanted stockpiles. Huang Qifan, director of Shanghai's economic commission, says in a published report that the city, whose economy is dominated by the shipbuilding, steel, automotive and textile industries, has lost 1.4 million of the 5 million manufacturing workers it supported several years ago.