Scheme 1, the load is 3 tons, which requires 8.4/3=2.8 days ≈3 days, and the freight is 300×3=900 yuan.

Option 2, with a load of 3.5 tons, requires 8.4/3.5=2.4 days ≈3 days, and the freight is 330×3=990 yuan.

Scheme 3, with a load of 4.5 tons, requires 8.4/4.5≈ 1.87 days ≈2 days, and the freight is 380×2=760 yuan.

Obviously, choose a load of 4.5 tons.