Extending gains for the fourth straight session, the Sensex at the Bombay Stock Exchange rose 80 points, or 0.4 percent, to a 3-week high of 18,492 on Tuesday on continuing FII inflows, amid firm regional bourses. The Sensex had already rallied more than 860 points in the previous three trading sessions. The Nifty at the National Stock Exchange added 19 points, or 0.3 percent, to also touch a 3-week high of 5,545.Stock markets in Japan, China, Hong Kong, and Singapore rose between 0.1 percent and 0.7 percent.