'Add' in the Bible

Woe to Ariel, to Ariel, the city where David dwelt! add ye year to year; let them kill sacrifices.

Woe to the rebellious children, saith the LORD, that take counsel, but not of me; and that cover with a covering, but not of my spirit, that they may add sin to sin:

Go, and say to Hezekiah, Thus saith the LORD, the God of David thy father, I have heard thy prayer, I have seen thy tears: behold, I will add unto thy days fifteen years.