Billionaire Li Ka-shing agreed to buy Duet Group in a A$7.4 billion deal, sweetening an earlier offer, as the Hong Kong tycoon seeks to expand his infrastructure assets in Australia to diversify away from Europe. In the revised bid, endorsed by Duet, investors will receive A$3.03 for each share in the energy company after including a newly announced special dividend of 3 cents a share, according to statements from the companies.