how do i get this? do i set the equation equal to one another?

ABC Freight operates two types of trucks. Truck type I, which has capacity 6400 cubic feet, has a fixed cost of $850 and a variable cost of $0.8 per mile. Operating costs for a trip for Truck type II, which has a capacity of 3000 cubic feet, consist of a fixed cost of $560 and a variable cost of $1.2 per mile. For shipments of up to 3000 cubic feet, what trip distance, in number of miles, would justify using truck type I? Specify only the amount. e.g. 3000