Sirius XM Holdings Inc. said it will acquire Pandora Media Inc. in a $3.5 billion deal, helping the satellite-radio company expand into online music. The all-stock transaction values Pandora at $10.14 a share, about 12 percent more than the company’s closing price on Friday. Sirius already has a 15 percent stake in Oakland, California-based Pandora, the companies said in a statement Monday. The combination will help Sirius expand beyond an audience that largely listens to the satellite radio company’s programs while driving.