Blackstone Inc. has agreed to sell its 49.9% stake in two Las Vegas hotels in a deal that values the properties at $5.5 billion. The New York investment firm is selling its stake in the MGM Grand Las Vegas and the Mandalay Bay to Vici Properties Inc., which owns the other 50.1% stake in the properties. Blackstone would receive $1.27 billion in cash, and Vici would assume Blackstone’s share of some $3 billion in debt. The sale would bring a profit of more than $700 million for Blackstone in less than three years.