I agree, the question is over-simplified - it wouldn't work for real in an engine shop, the definitions are a bit "loose".
This "total volume" assumes a perfectly flat piston, most aren't.
I missed the book answer of 6:1, yeah it can be worked out sorry.
The piston either being domed, flat, or dished doesn't matter, we now have enough information to work out the combustion chamber volume, etc.