Either you don't have that package, or it's out of date. Looking at the page, there are links for two other packages. Download them, going from right to left.
Linux Mint 8 RC1 = Nice
'apt install' can be used on Linux Mint as a shortcut for 'sudo apt-get install'. 'apt x' can be used for various other apt commands as well.
When a problem is solved, please add [SOLVED] to your thread title.