It is, at the pole, but that is not what the question said.
It says:"where the earth convergence between 2 points located on the parallel 60°N is 20°". If the earth convergence is 20° at 60N, the earth ch long is 23.09º.
If the question had said "chart convergence", I would have agreed with you.
As for dungfunnel, this forum is not "wannabes". Experienced knowledgeable pilots pursue subjects well beyond ATPL level here. A lot of people (but obviously not you) are interested in this knowledge for its own sake, not just to pass exams.
In any case, this question cannot be answered using ordinary ATPL syllabus knowledge - which is why I suspect that WhiteKnight may have it wrong - unless, of course, it comes from another source altogether and he has not got exams in mind.