At 55 miles per hour, he travels 55 miles in every hour. So, in 2 hours he goes 55 x 2 miles, or 110 miles.
In the same way: at 70 miles per hour he goes 70 miles in every hour, and he only travels for an hour, so he goes 70 miles.
Going 50 mph (miles per hour) for 2 hours, he travels 50 x 2 miles or 100 miles.
Add these numbers up: 110+70+100 = 280.