Algebra world problem help

A cattle train left the station and traveled east at an average speed of 40 km/h. Some time later a diesel train left traveling in the opposite direction with an average speed of 50 km/h. After the cattle train had traveled for six hours the trains were 390 km apart. Find the number of hours the diesel train traveled.

Please explain how you got the answer!

The cattle train traveled for six hours at 40 km/hr
So it went 240 km.
At six hours the trains were 390 km apart. So the
diesel train went 390 - 240 = 150 km.
It travels 50 km/hr, so it traveled for 3 hours.

40*6=240
390-240=150
50x=150
x=3
so the diesel train traveled for 3 hours

50(6 - x) + 40 * 6 = 390

300 - 50x + 240 = 390

540 - 50x = 390

-50x = -150

x = 3

you left a part out cause all you can say is that the train has 660 km to finish

you left something out, all I can say is
less than 6 hours