Give the step-by-step reasoning process and then the final answer. Jeff was driving to the capital city to attend a conference. At first, he was driving at 80 miles/hour for about 6 hours, then the speed limit changed and he had to slow down to 60 miles/hour, and so he drove at this speed for 4 hours. Then he made a stop at a gas station. Once the car was full of gas, he drove at 40 miles/hour the rest of the trip for 2 hours. How many miles did he travel?
In the first stretch he drove 80 miles / hour x 6 hours = 480 miles. In the second stretch he drove 60 miles / hour x 4 hours = 240 miles. After the gas station he drove 40 miles / hour x 2 hours = 80 miles. In total he drove 480 miles + 240 miles + 80 miles = 800 miles.
The final answer: 800.