What is the time period when they will clear of each other from the moment they meet?

It will be impossible for two trains 137 metres and 163 metres in length to meet when they are running towards each other on parallel lines, whether one is at the rate of 42 kmph and another at 48 kmpb or any other speed. This is because parallel lines never meet.

This may be a trick question, perhaps, testing not your ability to perform mathematical calculations but your understanding of the concept of 'parallel' or your ability to cut through extensive verbalisations to analyse the essence of a problem. This is what 'cutting to the chase' means.