National Can, Chicago, said its directors approved a $42-a-share buy-out offer by Triangle Industries, New Brunswick, N.J., and recommended that its shareholders tender their share under the offer . . . Chicago-based Sara Lee Corp., formerly Consolidated Foods, said it has agreed to buy 1.8 million of its common shares from the estate of its deceased founder, Nathan Cummings . . . Kaypro Corp., Solana Beach, Calif., introduced its new Kaypro 2000 full-function, lap-top computer, which is priced $2,000 and is IBM compatible . . . The American Iron and Steel Institute said steel production for the week ended April 6 fell to 1.796 million tons, down 4.4% from the week before.