(1) The cart is loaded with 4 cars, and the cart is loaded with 1 car. 4×6+4=28 tons

The big car is loaded with 2 cars, and the small car is loaded with 4 cars. 2×6+4×4=28 tons

There are seven cars in the car. 4×7=28 tons

(2) The big car is loaded with 4 cars, and the small car is the most economical.

4×800+600=3800 yuan