$500$ is the predecessor of $499$.

$7000$ is the successor of $6999$.

$458+639=639+$_____

$864+2006=2006+$_____.

$1946+$_____ $=984+1946$

$8063+0=$_____

$53501+(574+799)=574+(53501+$_____ $)$

Add $16509$ and $114$ and check by reversing the order of the addends.

Add $2359$ and $548$ and check by reversing the order of the addends.