m/s will be transcribed in Nemeth, according to Rule 4.4.10 since the slash means “per”. Rule 10.3 of the Nemeth Code states that the English-letter indicator is used before an abbreviation which consists of one letter. So m and s will each require an ELI.
Whether the variable r needs an ELI depends on the preceding material. Can you provide more context?
– Lindy