Why is there a hypen after TV and Working? Please explain

Tolley divided the sentences into two by replacing the hyphen with a period.  The sentences could also be corrected by replacing the hyphen (or period) with a semicolon. The semicolon is used to link two closely related, but complete independent clauses.

Your hyphens probably found their origin in something called the em-dash. Twice as long as a hyphen (give or take), the em-dash is sometimes used to replace commas or (rarely) semicolons to indicate a greater than normal pause in speech or thought ... or to emphasize something . Em-dashes are never used to replace periods. On typewriters, em-dashes were made using two hyphens "--".

My teachers told me to avoid using em-dashes until I had mastered the use of commas. Good advice.