Explanation:

Let the speed of the faster train be 'S' kmph

Then speed of the slower train will be '(S-5)' kmph

Time taken by faster train = 350/S hrs

Time taken by slower train = 350/(S-5) hrs

350/s−5 − 350/s = 2 hrs 20 min = 2 1/3 = 7/3

S = 30 km/hr.

Hence, option 2 is the correct answer.