The correct answer is the last sentence: The solution is clear - we simply need the courage to follow through.
The dash is a mark of punctuation used to set off a word or a phrase after an independent clause or parenthetical remark (work, phrases, all that interrupts a sentence).
The dash (the em dash) is significantly longer than the hyphen. We use this dash to create a strong break in the structure of the sentence.
The solution is clear, here we introduce the dash because we want the listener to pause and anticipate the rest of the sentence. By creating this break, we have the listener's whole attention and we can express the meaning of the sentence more clearly and directly.