Nina owns a used car lot. She signs and sends a fax to Seth, a used car wholesaler who has a huge lot of cars in the same city. The fax says, "Confirming our agrmt-I pick any 15 cars fr yr lot-30% below blue book." Seth reads the fax, laughs, and throws it away. Two weeks later, Nina arrives and demands to purchase 15 of Seth's cars. Is he obligated to sell?