CBS and Viacom are expected to announce a merger soon

CBS Corp. and Viacom Inc. may be done keeping investors waiting.The media giants are expected to announce a merger as soon as Tuesday, the culmination of years of on-again, off-again discussions.They’ve agreed on an exchange ratio of 0.59625 a share of CBS for each of Viacom’s for the all-stock merger, according to people familiar with the situation. At this level, a deal would peg Viacom at around its current market value of close to $12 billion. The agreement struck between the com