Six of Pentacles is the card of exchange, of sharing and interaction. It's also a card of harmony and balance, so it often appears after times of strife. The King of Swords symbolizes the maturity of logic. For that reason, he has a bad reputation when it comes to feelings and indeed, this King will choose to do what is objectively right rather than what feels right. The King of Swords is associated with justice, communications, decisions, emotional detachment. The Six of Pentacles and the King of Swords is a combination that shows fair judgement and a balanced interaction or agreement.
To understand the elemental relationships between the cards, we should always take into account their actual meaning. The elements of the cards are Earth (Six of Pentacles) and Air (King of Swords). This combination gives poor results, as the Air card is trying to motivate the Earth card to move, but they can end up going around in circles, like a vortex of rotating air and dust. However, the King's judgment is fair and clear and that means he will be able to manage the situation in a balanced and controlled manner.