freight train and an express train leave towns 390 km apart, traveling toward one another. The freight train travels 30 km per hour slower than the express train. They pass one another 3 hours later. What are their speeds?
Their combined speeds, (x) and (x-30) cover the 390 km in 3 hours
3 hours * x km/hr + 3 hours * (x-30)km/hr = 390 km
3x + 3 (x-30) = 390
solve for 'x' the speed of the express, then ffreight = (x-30)