Question

(LC)Which sentence below shows correct use of an em dash? He didn’t hear the doorbell broken – since last week when – the delivery person arrived. He didn’t hear the door-bell broken since last-week when the delivery-person arrived. He didn’t hear the doorbell – broken since last week – when the delivery person arrived. He didn’t hear the door-bell broken since last week – when the delivery person arrived.

Answer 1

The correct answer is: He didn't hear the doorbell - broken since the last week - when the delivery person arrived.
Em dash is usually used instead of a comma. 

Answer 2

The answer to the question above would be that the sentence that shows the correct use of the em dash is the following one: He didn't hear the doorbell  – broken since last week – when the delivery person arrived.

The em dash is a really versatile punctuation mark: It can take the place of commas, parentheses, or colons. In this case, I believe that the em dash has been used to replace a pair of parentheses. Dashes are considered more intrusive than parentheses, so you generally use them when you want to draw attention to the parenthetical content. In this case, by means of the use of the em dash, the writer emphasizes that the doorbell has been broken for a week.