United Rentals, the largest equipment rental company in the world, will buy RSC Holdings in a $4.2 billion cash-and-stock deal that includes the assumption of $2.3 billion in debt.

RSC shareholders will receive $10.80 in cash and 0.2783 shares of United Rentals stock per RSC share, a 58 percent premium over the company Dec. 15 closing price. Oak Hill Capital partners, RSC’s largest stockholder, has agreed to vote its 33.5 percent share in favor of the transaction. When the deal closes, expected in the first half of 2012, RSC stockholders will own approximately 30 percent of the combined company.