There is a hyphen in phrases like "100-year", because they precede whatever they are modifying, like a "100-year flood". In general, two-word phrases are hyphenated when they are used as adjectives and precede the term they modify.
No.
Yes
No it doesn't require to be hyphenated.
part before hyphen is model number for 1969 4 hp.
If you're using the phrase as an adjective (example "I hate the end-of-the-year audit!") then it will definitely need the hyphens. Otherwise, the hyphens are incorrect.
B
Four-year should be hyphenated but not institution.
Yes it should be hyphenated.
There was no year zero century or year zero. 1 AD immediately followed 1 BC. The first century AD immediately followed the first century BC. There was no century between them.
-1840
It looks like a date. It could mean 3 November 2008. Then again, it could mean 11 March 2008.To specify a system for writing dates, people sometimes use a format such as yyyy-mm-dd, which means "four digits for the year, followed by a hyphen, two digits for the month, hyphen, two digits for the day".
In a citation within the text, the journal name appears in italics followed by the volume number, issue number in brackets, page numbers, and publication year. In the reference list at the end of the document, the journal name is also in italics, followed by the volume number, issue number in brackets, page numbers, and publication year.