Here is the sentence I'd like to ask you about:
"After the fire of 1837 in the Winter Palace, the Military Gallery of 1812 was extended by 6 metres".
Do we need the preposition "by" after "extended"? The meaning of the sentence is that the gallery became 6 metres longer than before.
Thanks a lot
You could get away without it in informal speech, but I would definitely use by in writing.