A manufacturing company ships its product in two different sizes of truck trailers. Each shipment is made in a trailer with dimensions 8 feet×10 feet×30 feet or 8 feet×10 feet×40 feet. If 30% of its shipments are made by using 30-foot trailers and 70% by using 40-foot trailers, find the mean volume shipped per trailer load. (Assume that the trailers are always full.)