From Ubuntu Terminal screen (Applications > Accessories > Terminal), type:
taufanlubis@toshiba:~$ sudo apt-get install stax
Reading package lists… Done
Building dependency tree
Reading state information… Done
The following packages were automatically installed and are no longer required:
libmyth-0.20 libsvga1 quake2-data
Use ‘apt-get autoremove’ to remove them.
The following NEW packages will be installed:
0 upgraded, 1 newly installed, 0 to remove and 0 not upgraded.
Need to get 566kB of archives.
After unpacking 811kB of additional disk space will be used.
Get:1 http://archive.ubuntu.com gutsy/universe stax 1.0-13ubuntu3 [566kB]
Fetched 557kB in 21s (25.9kB/s)