If he goes 140 miles in 2 hours, then in 6 hours he would go 420 miles. 420 miles is not equivalent to 490 miles, so he would not reach his destination on time.
The model predicts 75m. The earlier estimate was 1.6km (1 mile) and was close to a given point. The model would only be a good predictor during the sky crane phase of landing.
