Suppose you own a courier service and you use two types of delivery vehicles $-$ Model A$,$ which costs $$30000$ to purchase, and Model B$,$ which costs $$50000$ to purchase. You have a budget of $$300000$ for the purchase of new vehicles. What is the opportunity cost of one Model A vehicle? $3/5$ of a Model B vehicle X $5/3$ Model B vehicles $3$ Model B vehicles $5$ Model B vehicles