Suppose that France and Germany each produce wheat and cars. By using all available resources and technology, France can produce at most 30 units of wheat and 12 cars per year, and Germany can produce at most 25 units of wheat and 15 cars per year. Suppose that, to protect the domestic car industry, the government of France decides that France will produce 6 cars per year. Assuming that opportunity costs are constant, at most how many units of wheat can France produce?