"How many dead were there?"
Translation:Kolik bylo mrtvých?
The 'there' in the question isn't referring to a place, but a state of past existence. 'There were XXX dead' as opposed to 'There (location), there were XXX dead.' So, the 'tam' in your answer isn't necessary.
But the way the question is written,'there' could be referring to a place. It could equally mean 'How many were dead?' or 'How many dead were in that place?'
There is not way to know if there is place or "at that time". I also thought if was referring to some place