A shipping company need to transport packages by either truck or car. A truck can transport 50 packages per trip while a car can transport 30 packages per trip. In addition, a truck uses 20 liters of gas per trip while a car uses 15 liters of gas per trip. There can be at most 5 truck trips made and at least 30% of all the trips must be made by car. The company needs to transport at least 500 packages. How many of each transportation should they use to minimize the total amount of gas consumed?