How do you say "I think the answer is _____" in German?
Perhaps this webpage on coordinating conjunctions and subordinating conjunctions may help. :) dass is a subordinating conjunction, so the verb goes to the end of the subordinate clause.
I think Klastiron answered yor question about the comma already. But in your question you changed the position of the "answer" as well.
In German you can say:
"Ich denke, dass die Antwort _ ist." or "Ich denke, die Antwort ist ___."
With the later the more common answer in German.
In common or colloquial language we would rather say
- "Ich denke, die Antwort ist..."
- "Ich denke, die Antwort lautet...".
In your example, you have to add a comma after "denke" and be aware for the changed word order:
- "Ich denke, dass die Antwort .... ist."
Here you also can say 'lautet' instead of 'ist'
Edit: Ups, grantagi already mentioned it :-)