Did all the B shares convert to A class? It should say on your 1099B statement what fund the shares were sold out of. A and B should be be listed separately if you sold any left over B shares.
Did you sell all your shares of both? If not you might have some work to do to figure out the cost basis since you reinvested the dividends. The reinvested dividends bought more shares and you can add the $ back into your cost so your gain will be less.
