a trucker hauls citrus fruit from Florida to Montreal. Each crate of oranges is 4 ft3 in volume and weighs 80 lb. Each crate of grapefruit has a volume of 6 ft3 and weighs 100 lb. His truck has a maximum capacity of 300 ft3 and can carry no more than 6800 lb. Moreover, he is not permitted to carry more crates of grapefruit than crates of oranges. If his profit is $2.50 on each crate of oranges and $4 on each crate of grapefruit, how many crates of each fruit should he carry for maximum profit