Algebrator
From SlugWiki
The TI 89. Next to google, its "the best thing since sliced milk..."
Many problem sets have been salvaged at the last minute, thanks to the algebra abilities of the TI 89. They replace the abilities we abandoned freshman year.
And yes, you can use it to find (273 - 9).
It even does most unit conversions. If only it had better integral tables.
Thank you, Algebrator