안녕하세요! :) Hi~! Actually "~는 거라고 풀수가 있지" sounds little bit weird to me and this is because, considering the meaning of "풀 수가", it sounds like "you can solve that ~" You indicated that it was translated as "you can say that" so instead of former one, "~라고/이라 말할 수가 있지" would be better phrase. Lastly, as for interchange, you can use both of them. But honestly, former one is more likely to contain your confidence. And the last one is sounds like you are just deliverying some pharses to someone. I'm little bit worry about my reply's grammer so that you may have some trouble to understand. But no matter what ,I really hope that this could be helpful to you! :)