nina? >> pauline, the four remaining u.s. republicans competing for the company's presidential nomination locked horns again. during cnn's debate in florida, they appeared to put aside their differences over the front rounr in mitt romney's wealth and the tax he has or has not been paying on it. he released his tax returns this week under pressure by this man, newt gingrich. as president barack obama calls for higher taxes on the rich, romney defended both the relatively low rates he pays and the motives behind his money making. take a listen. >> i'm proud of being successful. i'm proud of being in the free enterprise system that creates jobs from other people. i'm not going to run from that. let's put behind this idea of attacking me because of my investments orman any and get republicans to say, you know what? what you've accomplished in your life shouldn't be seen as a detriment. it should be seen as an asset to help america. >> and the florida primaries will take place on tuesday next week. >>> coming up next on "world business today," we speak to one of russia's richest men at the world economic men in