7. a distribution centre sends three different types of parcels. one consignment has 6 small, 8 medium and 9 large parcels which cost $173.20 to post. another consignment has 7 small, 13 medium and 17 large parcels with total postage $291.05. a large parcel costs twice as much to post as a small one. work out the total cost of posting 3 small parcels, 9 medium parcels and 2 large parcels.