Translation:We are going on the ferry and the train.
In Welsh we need the definite article here, there is no literal equivalent of 'by ferry'. Since the most common translation in English is 'by' we've added that as an option.
There are 55 possible correct translations of this sentence into English on the database now, over 30 of them using 'by'.
It's however easier to see the construction of the Welsh sentence by writing the correct English of 'We are going on the ferry and the train'
So the above is noted as the preferred translation while all the others are accepted as valid alternatives.