An express train takes 4 hours and a local train 5 hours for the same trip, the express being 12 mph faster. The local train's speed is:

1. Both cover the same distance. 2. 5r equals 4 times r plus 12. 3. So r is 48 mph. _Source: OpenStax Elementary Algebra 2e, Chapter 3, Uniform Motion Applications (CC BY 4.0)._