A customer wants to order a combination of oak and pine seedlings. The customer wants at least 8 seedlings to include at least 5 pine seedlings. The box used for shipping can hold no more than 18 pounds. One oak seedling weighs 1 pound and costs $3 to ship. One pine seedling weighs 2 pounds and costs only $2 to ship. What combination of oak and pine seedlings should the customer order to minimize shipping costs?