There's not a specified number. That's not how marking works.
We can't really be sure what impact this would have on your mark because they haven't asked for two RTs in so long that we can't know how this would be included in the marking criteria.
For comparison, if you are asked for one RT in Mod C and use none, then you will probably score 9-12/20 if your essay is otherwise reasonable.
However this is all beside the point because the chance that you'll be asked for 2 RTs is very remote. A prudent student will have a second one anyway but it's extremely unlikely that they'll ask for two.
