Tony drives 4 hours in all, 208 miles on the interstate and 40 on country roads, going 15 mph faster on the interstate. His country road speed is:

1. At 50 mph the 40 miles take 0.8 hours. 2. At 65 mph the 208 miles take 3.2 hours. 3. Those add to 4 hours, so 50 mph is right. _Source: OpenStax Elementary Algebra, Chapter 8, Solve Uniform Motion and Work Applications._