9 carts, 8 carts, 2 carts, 7 carts, 4 carts. Six big cars and six small cars. Five big cars and nine small cars. 4 carts 1 1 carts. Three carts 13 cars. 2 carts 16 carts. 1 cart and 18 cart. Twenty cars. Calculate the price of each scheme, compare them, and get the scheme to save money. For example; 6 cars are big and 6 cars are small; 6 * 400 = 2400 6 *180 =10801080+2400 = 3480 yuan.