Question

Which two sentences correctly use a dash? Most of the working population today is troubled—by lack of sleep. You need to sleep 6—8 hours daily to maintain a healthy body. The secret to improving your productivity is simple—get a good night's rest. I found something unexpected in my trash can—a litter of raccoons

Answer 1

-The secret to improving your productivity is simple—get a good night's rest.

- I found something unexpected in my trash can—a litter of raccoons

Answer 2

The two sentences that correctly used a dash are the following:
- The secret to improving your productivity is simple--get a good night's rest.
- I found something unexpected in my trash can--a litter of raccoons. 
Dashes are used in the sentence when there is an added information that is not generally part of the sentence.