A business has $15,000 to spend on airline tickets to travel to a conference. It wants 27 of its employees to attend. The business wants to buy as many business-class seats as possible. The business-class seats cost $700. The economy-class seats cost $375. Create a system of equations that models how many of each type of ticket the business should purchase.

700x + 375y = 27
x + y = 15,000
x + 375y = 15,000
700x + y = 27
700x + y = 15,000
x + 375y = 27
700x + 375y = 15,000
x + y = 27