xrcalc is a free calculator for XFCE / Xubuntu / Ubuntu / (debian), which doesn't require any other dependencies.
(By the way, the result underneath in the screenshot isn't wrong).
The full sum was 52.30001 x 3 / 28.12265 = 5.579133 but you can't see the first line in the screenshot.
This is for Xubuntu Linux, using the XFCE 4 window manager, but will probably work on Ubuntu or anything based on Debian Linux.
If you have any suggestions, please get in touch via email. Many thanks.