Francesco Guerrera: A simple solution is staring the likes of Deutsche Bank AG, BNP Paribas SA and Banco Santander in the face: large, decisive, increases in capital through equity sales that would allay investor concerns and boost balance sheets. With the year-end results almost all out of the way, banks should start raising capital soon. The experience of the U.S. financial crisis shows that in stressed times capital infusions can cure or mask many ills and buy valuable time to restructure businesses.