Distance = speed × time

Given, passenger train takes 3 hours less for a journey of 360 km, if its speed is increased by 10 km / hr from its usual speed.

Let the speed be ‘s’ and time be ‘t’.

⇒ st = 360

⇒ t = 360/s

Also, 360 = (s + 10)(t – 3)

⇒ 360s = 360s + 3600 -3s² – 30s

⇒ s² + 10s – 1200 = 0

⇒ s² + 40s – 30s – 1200 = 0

⇒ s(s + 40) – 30(s + 40) = 0

⇒ (s – 30)(s + 40) = 0

⇒ s = 30 km/hr