1. The problem statement, all variables and given/known data A passenger train is approaching a railway crossing from 105m to the east, at 54km/h. Meanwhile a train approaches from 140m to the north, at 72km/h. How fast is the distance between them changing after 5 seconds? 2. Relevant equations Pythagorean Theorem? 3. The attempt at a solution It looks to me that there are four constants in this question, namely: The distance and velocity of the train which are 140m and 72km/h respectively. The distance and velocity of the car which are 105m and 54km/h respectively. I drew a right angled triangle and labeled x the car distance on the horizontal and y the train distance on the vertical with z marked on the hypotenuse. I guess before i go further, i need to know if i am setting up this problem right first, because i am confused as to how to setup all the given data. Help?