Bardin, congrats to your DS! May I ask which external help if any did you use to tackle those specific questions?
Send me a personal message (the forum rules don't allow you to post recommendations) and I can say who we used - it was a class set up rather than a single tutor, which may not suit everybody.
What I meant was that if you have the same (genetic) mind set as your child, you may not be able to help much with the ones they get wrong - as you may not understand any bette rthan they do, even when the answer is given. Similarly if there is a type of question you and yyour child struggle with, it would be good to get a 'second opinion - from a tutor or intelligent friend.