'5 years experience' vs '5 years of experience'?

English as a Second Language English Vocabulary, Grammar and Idioms
1

Hi,

Which of the followings is correct:

“She has had 5 years experience in the oil industry”
“She has had 5 years of experience in the oil industry”

Besides, is my above use of ‘following’ in plural form correct?

Thank you very much.

2

You must add an apostrophe to “5 years” if you don’t use it with “of.” “The following” should not be plural.