Here is an AppleScript code that seems to be working:
set query to "{query}" as text
set base_em to 16
set calculated_em to (query / base_em) as real
set the clipboard to calculated_em as text
And here is the workflow I did to test it: download now
This workflow mutes the system volume with the Keyword mute, meaning that all sound coming from the computer is stopped. Typing mute again will re-enable sound. It's pretty simple, but effective:
Remember to disable the iTunes mute Keyword, if previously enabled: Preferences > Features > iTunes > Keywords > Mute iTunes
If you want a finer degree of control, you could also rig it to work in conjunction with the iTunes mute Keyword if this workflow's Keyword is changed to something different, say "muteall".